This review is for single-player only.
I've defended the Call of Duty series against the hyperbolic criticisms it has received. It's not the worst thing to ever happen to gaming, despite the panicked cries of some hypersensitive individuals. And yet, although my contrarian streak often leads me to defend the unfashionable, I will never defend the indefensible. Modern Warfare 2 is the point in my Call of Duty playthrough where all the cracks began to show. From the gameplay to the story, every possible flaw in the Modern Warfare series was highlighted in Modern Warfare 2.
The one exception to this is the graphics. The game looks good today; I imagine that it looked great when it came out (I was more into retro gaming c. 2009, so it wasn't on my radar). Unfortunately, I never really got to appreciate this, because it is all but impossible to tell at any given moment what is going on. The poor readability of Call of Duty is on full display here; battles are a mess of sound and fury, signifying nothing. The moment I figure out where my enemies are shooting from, the Blood Screen ™ pops up and smears my monitor with red watercolor paint for what seems like 5 minutes. I spent about half of my playthough crouching behind objects, waiting for the blood to be wiped off the screen. Ah, the most fun part of playing an action game--standing still in one place waiting for something to happen. It was like watching one of those John Cena wrestling matches where he spends half the match lying on the mat. And unlike third-person cover shooters (e.g. Gears of War) where you can gauge the state of combat while you are behind cover, in COD you can't peek out of cover unless you want to get shot again. You are stuck, staring at a texture that is either beige, brown, gray, dark green, or some mixture of those for a solid minute. "This would be a nice color for the kitchen cabinets" you think to yourself as the Admiral from Mass Effect screams to you about getting to the Burgertown so you can pick up some RPGs.
MW2's level design is less linear than the previous games, but somehow this makes the gameplay worse. The series' trademark cover-shooting and braindead enemy AI work decently with linear levels; it feels like a natural extension of rail-shooter games like Time Crisis, with some cover-to-cover movement thrown in. But in the more open environments (especially in the favela and the suburbs in "Wolverines") running and gunning or even moving from cover-to-cover is an exercise in frustration, and not the fun kind of frustration. I found myself forced between getting hit and seeing that stupid Bloody Screen ™ or staying in one spot for a lifetime. Every non-linear level involved me cheesing it to win. Skill issue, I suppose, but it felt wrong (although vaguely satisfying) to spend half of "Wolverines" sitting on top of the McAllisters waiting for the Russians to climb up the ladder so I could strike them down, one by one.
To break up the frenetic monotony of the base gameplay, we have our special levels: turret sequences, stealth sequences, and drone-strike/airstrike sequences. Turret gunning is aways fun for about 30 seconds, but these could be subtracted from all shooter games past, present, and future, and I would never notice the difference. Stealth in this game is ludicrous--enemies either see you or don't, lines of sight, cover, and light levels be damned. And the drone strike/air strike sequences are flat-out boring. I suppose they are there to train you to use the drones or call in airstrikes in the multiplayer mode, but they are like the world's slowest and simplest game of whackamole in single-player. They do add an element of realism (to my knowledge, a lot of U.S. military tactics since Vietnam boils down to "find enemy and call in airstrike"), but they don't add to gameplay.
Roller-coaster shooters are only as good as their setpieces and the game fumbles in this regard. I'll talk more about the story in my mini-essay below; suffice it to say that it is so nonsensical, convoluted, and poorly told that the setpieces hold no weight. The bombing of the Eiffel Tower in MW3 or "All Ghillied Up" in MW worked as setpieces not only because they were thrilling in their own right, but because they made sense in the story. You really got to feel like you were living the movie, not just seeing the climactic sacrifice or the insightful flashback, but actually experiencing it. There is nothing like that here (apart from "No Russian," which I will also talk about below). The closest thing is the attacks on suburban America; speaking as an American, watching close quarters warfare occurring in a place that is reasonably familiar to me was quite chilling. Unfortunately, the game doesn't really do anything with this. The one good setpiece comes at the end, during the final battle between the evil general and Captain Price. It's probably the only time I have ever been engaged in a quick-time event. Say what you will about Infinity Ward, but when they delivered, they really delivered. Unfortunately, it's just one moment in a rather weak campaign.
Overall, considered as a single-player game only, Modern Warfare 2 is the weakest of the trilogy and somewhere between a 2.5 and 3 star game. I would recommend playing the Spec Ops missions instead of the campaign, as they tend to be more varied and are fun to play in co-op mode.

"No Russian" Analysis:
This mini-essay touches on some political themes and contains spoilers for the Modern Warfare trilogy and Spec Ops: The Line.
The Call of Duty series is often criticized as propaganda, and there actually is some truth to this, as Activision has worked with the U.S. government to assist with recruiting efforts. To my knowledge, this partnership started after the end of the first Modern Warfare trilogy, but it was an obvious matchup.
I remarked in my review of Modern Warfare 1 that it seemed like sadistic propaganda to me, a game designed to train the player into becoming a thoughtless, heartless killer. I initially had that thought about Modern Warfare 2 near the beginning of my playthrough. As I got further into it, though, I changed my mind. I'm not sure what the point of Modern Warfare 2 is, and I don't think the game's writers were sure either. My problem with Modern Warfare 2 isn't that it's propaganda. My problem with Modern Warfare 2 is that it is isn't really anything. I don't dislike its storyline because it stands for ideals that I hate. I dislike its storyline because it doesn't stand for anything.
For propaganda to really work, it has to have an internal consistency. Medal of Honor 2010 is a propaganda piece. Americans good guys, Taliban bad guys (they literally tell you this about 30 times in-game). You shoot at hadjis from a chopper while cheesy rock music plays. It's about as on the nose as it can get. Any moral ambiguity in its story is something that was brought to the work by the viewer. The point of propaganda is to make a point; one can objectively appreciate a work of propaganda for clearly making the point while hating the point being made. But in order to make the point, there must be a consistency to the story and tone.
Modern Warfare 2's campaign is all over the place. Impactful events happen without ever giving us a moment to breathe in and take stock of what is happening. For example:
• Russians invade the U.S. and turn the suburbs of D.C. into a warzone. We don't really see the effects of this on civilians. We don't get a moment to think about how terrible this is. This is the perfect moment for propaganda. This is the part of the story where you should see the eeeevil Russians lining up civilians; Ivan Badnik gives a speech about how the Americans are weak and soft, only for the badass ex-Marine in the crowd to give him the one-finger salute. T The story practically writes itself at this point. Instead, what we get is a wild goose chase through suburbia without a satisfying setup or payoff.
• Soap and his buddies capture a guy in Brazil, then torture him offscreen. This is implied in a blink-and-you'll miss it moment. I disagreed with the torture scene in Modern Warfare, but at least there it sort of had a point. Here, you don't even get any intel out of the guy. Is this supposed to be supporting torture? Is it setting up Task Force 141 as bad guys? As pragmatic hardliners who will do whatever it takes to win? As once good guys who have been pushed to the edge and are now fighting brutality with brutality? How am I supposed to feel about this? Horrified? Amused? Don't know. Don't care. It makes propaganda sense to have "justified" torture as a plot point, but to work as propaganda, it has to be set up and paid off. In this game, we don't even get any useful intel from the guy who gets tortured.
• You have a moment where you have to fight in the White House. This should have been a huge, climactic moment. It is not. We don't even see the President. This should have been the moment where PUSA shows up and rallies the troops. Imagine this scene: you and the troops show up to escort the President to safety, but instead of following you to his bunker, the President (who is of course ex-military) picks up a rifle and joins you. "I'm coming with you, Sergeant. That's an order from your commander-in-chief." It would have made more sense to go the propaganda route with this scenario than to do whatever it was that you did in the mission (I honestly forgot).
When the game isn't being underwhelming it's being tonally inconsistent. The game tries to give a semi-grounded, gritty portrayal of military combat, yet it features a nuke being detonated in space that somehow destroys a space station on the other side of the planet yet also doesn't hurt any of the Americans beneath it. It begins with a general giving Medal of Honor-esque speeches about freedom and fighting for what is right, and ends with that general betraying the US for the most convoluted of reasons. It features torture as a throwaway reference rather than taking a stand for or against it. It has you play assistant to the world's greatest action heroes fighting the villainous Russians, yet whenever you die, about 75% quotes that show up on screen are about the futility of revenge, the idiocy of blind patriotism, and the horrors of war. What is the game trying to communicate? What is the message here? Who is the target of these quotes? The Russians? The evil general? The player character? Me, the player? What am I supposed to be feeling? The game doesn't know what it is trying to say.
Nowhere is that more evident than in the infamous "No Russian" mission--possibly the trashiest event in a mainstream game.
To put things into perspective,my body count in video games is somewhere between George W. Bush and Josef Stalin. Most of my favorite games are very violent. I loved chainsawing the locusts in half in Gears of War and blowing up enemies in Rage 2. I wasn't bothered by the interactive torture scene in Far Cry 3 or the white phosphorus in Spec Ops: The Line. But "No Russian" disgusted me. It made me almost physically ill. Only the fact that I was playing through MW2 in an attempt to better understand Spec Ops: The Line made me avoid quitting the game in disgust. It was unjustifiable
Why "No Russian" disgust me when the white phosphorus in Spec Ops: The Line did not? Again, it comes down to the fact that Spec Ops: The Line was actually saying something with that moment. not Spec Ops: The Line spends quite a lot of time setting up the characters before the white phosphorus. We feel that they are real people with realistic motivations. We are not just told that the soldiers have to use the white phosphorus, but we are shown why. The soldiers are outnumbered and behind enemy lines. They are faced with a hostile force much larger than them that is blocking their only way out. It's made clear that the white phosphorus is the only way out. And the game makes sure that you know that this decision is not taken lightly, even before the big reveal--while you are calling in the strikes, you can see Walker's reflection in the screen, his face one of grim determination. Once you finish the segment, you see the consequences of your actions. And the entire segment fits in with the rest of the game. It is tonally and thematically consistent.
On the other hand, in "No Russian" you play a faceless, voiceless drone with no character development to speak of. There is no setup for the airport massacre--you hear General Shepherd giving a speech about doing whatever it takes to infiltrate Makarov, and then you are suddenly plopped into the middle of a massacre. There's no buildup where you gradually infiltrate Makarov's inner circle, making more and more moral compromises in order to get close to Public Enemy No. 1, before finally joining in the killing of innocent civilians. Nor is there anything during the event that signals to you that the spy has any qualms about gunning down a bunch of noncombatants. And once the mission is over, there's no reflection on what happened. We don't get time to process the event. We don't see any characters react to what happened. It's just another contrivance to speed the plot along. "No Russian" could have made sense as the climax to an established story arc; as a random mission at the beginning of the story with no setup and little payoff, it makes zero sense.
I suspect that "No Russian" was either thrown in for pure shock value or is a remnant of an earlier, more coherent script that was Frankensteined into the mess that exists in the final game. Nothing else explains why this tonally inconsistent and utterly tasteless mission made it past the cutting room floor. It has no message other than shocking the player and the general public.
And the craziest thing is this--Infinity Ward was actually able to put a moment into Modern Warfare 3 that accomplished most of what "No Russian" was trying to accomplish in a much more tasteful way. It's the brief cutscene where the dad is filming his family on vacation and the chemical attack happens. It's shocking in its own way, but it never forces the player to participate in any sadism. It takes its time to establish the characters before killing them off. It motivates the player. This is why we are fighting the Russian ultranationalists. This is why it is worth bombing the Eiffel Tower. This is why Price is motivated to kill Makarov. To prevent more innocent people from dying. It's still shocking, it borders on the edge of tacky, but it it actually makes a point.It's closer to what "No Russian" should have been. Instead of being a heartless killer just becuz, you should have been a civilian, running from the murderers in the airport, maybe finally getting killed by Private Whatsisname. This would have accomplished everything that "No Russian" kindasorta wanted to accomplish
• It would have shown how Private Whom finally became a hardened killer working with Makarov, compromising everything he stood for (like General Shepherd)
• It would have shown the events through the Russians eyes, allowing us to understand why they were angry enough at the Americans to launch an invasion.
• It still would have been shocking enough to get people talking and move units ("Did you hear about the game where you get killed in a mass shooting?")
So, in conclusion, I think "No Russian" was a terrible mission that made little narrative sense, has no justification and exists solely for shock value. It's disgusting, it's tacky, and even in retrospect it makes gaming look bad. And it brings to light all the narrative flaws of Modern Warfare 2's campaign: a story that condemns nothing, stands for nothing, says nothing, means nothing, and does all of this at an incredibly loud volume.