I'm conflicted on 5, because I really enjoy playing through it but there are some huge caveats. It lacks a lot of the frustrating bullshit found in some of the previous games; there is way less reliance on insta-spikes, pit enemies, and high health drones that force you to use your charge shot tediously. On the other hand, it has maybe the absolute worst weapons in the original hexology and the robot master skillsets are a little underwhelimng. The megabuster is the best weapon to use 99% of the time, charge shot or otherwise, and is even the preferred weapon for the lackluster final Wily boss.

The level design is also fairly bland and very "hold right to win" on some levels, very specifically Wave Man's. Cool concept, bad execution with the boat. There's also a way higher reuse of enemies, frequently just putting them in a vehicle that matches the robot master and filling a level with them.

Despite the misgivings, it's pace is quick, controls and gameplay from start to finish are consistent and tight, Proto Man being the "enemy" is cool, and most important of all, it still just feels fun to play. This ones Wily's Castle is one of my favorite ones as well. OST is better than 4's. It doesn't break new ground in the series, but it's an enjoyable and it's vastly over exaggerated how bad it is compared to some other entries.

Mega Man 5 isn't quite offensive, but it isn't very good.

Maybe it's just because this is the second Mega Man game with a Robot Master weapon that requires Mega Man to make direct physical contact with the enemy (Charge Kick in this case), but it's more obvious here than ever just how devoid of any "game feel" or any tactile sense of friction. It's not just because Mega Man lacks the movement options that would be introduced in the X games and beyond. The hitboxes, plain enemies, the lack of death animations beyond simple explosions; even compared to other popular NES games, nothing in classic Mega Man feels solid, there is no sense that anything in the game is an object existing in a space.

There are technically interesting setpieces, like the collapsing tower of the final Dark Man stage. The fact that the game manages to pull off parallax scrolling on the NES is technically impressive. In general it feels like style over substance, even moreso than what I think is already typical for the series. The first fight with Wily is probably the worse example, with the weird "shifting camera" effect altering the way Mega Man jumps: it is probably the clunkiest boss fight in the series thus far, even if it's far from the most difficult.

The difficulty in general was pretty low this time around, all things considered. Mega Man 5 continues the trend started with Mega Man 3, it is rather long. However, there is never any shortage of lives or E-tanks. The M-tank refills literally all weapons, and if you're low on ammo for most of your weapons the amount of time it takes to top them all off is kind of hilarious. By collecting a bunch of letters, mostly "hidden" in plain sight, you can unlock the special item Beat, a bird that automatically attacks enemies and bosses for you as long as you have the ammo for it.

The soundtrack isn't bad, but most of it is rather generic. It sounds like stereotypical 8-bit stuff for the mostpart, like a licensed Game Boy Color game. The boss theme is the most unexciting in the series so far, it's as if they know these fights aren't really intimidating anymore.

The boss weapons are really weird. You get two Wood Man-style orbital shields, and neither of them are very good. Crystal Eye and Charge Kick are basically just new versions of a couple of the worst abilities from Mega Man 3 (Gemini Laser and Top Spin). Charging the Mega Buster is only marginally more useful than it was in Mega Man 4, being particularly practical for a few bosses.

The ending is oddly abrupt, and the credits sequence lacks the soul that previous ones had.

There's no real reason to play this one instead of one of the others.

(Also played via Legacy Collection)
This is pretty much a lesser Mega Man 4 but it's still pretty solid and it does have some improvements over the previous games. The Dual Buster is incredibly satisfying and makes for the single best Mega Man game to do a Buster-only run, and it's a big improvement over the unpolished charged shot from the previous game. The visuals and sprite animations are even more detailed than Mega Man 4 and I applaud this game for being the only Mega Man game to make a good vehicle stage.

I guess what really brings the score down is because, like I said, it feels like a weaker Mega Man 4. It's not that remarkable of a game, the soundtrack is probably the weakest of the classic series and the Robot Master weapons are way too similar to weapons in previous games. Also the Robot Masters' weaknesses themselves, for the most part, don't really make any sense. Beat is cool, but it wasn't implemented in any interesting way. I guess it's pretty useful against the final boss because he's kind of a pain in the ass but other than that, I don't really see a reason to try to get Beat.

This is still a solid fun game with solid level design, solid bosses, and solid presentation but it just doesn't really do anything really big to stand out from other games in the classic series.