Okay, where do I even start... This game is really weird.

Why is it so long?

No, really. The question is not even out of annoyance. I actually don't think I've played a linear, almost seamless game that long. Especially when you consider how all events happen during one single day, the game feels like it purposefully drags time. Howlongtobeat says it takes 22 hours to complete it, it took me 18 hours, but I was just skipping a lot at some points, so the truth must be somewhere in between. There are some walkthroughs on YouTube that are 5-6 hours long, but that's just bullshit.

Why is it so long?

Lots of things that made you enjoy the game in the beginning become more and more annoying as time goes on. Source is great for such environments, yet the more time you spend underground, the more painful it is to look at. The game regains some of its momentum in the latter chapters, but again, you spend a lot of time in the dark. This is actually part of a bigger issue I have with the game...

I kinda hate the protagonist. His obsession with undeground sewers, tunnels and wasting time becomes more and more obvious the further you play, because why the fuck is he even doing half the stuff he's doing? Why is he so reluctant to just go back to the office? I generally don't like when games put you in situations where there's obviously an easy way out, but it's not achievable due to gameplay or story limitations. That's just bad design. You could've avoided doing that as a developer, but you still did. There were at least 3 or 4 times where the protagonist was LITERALLY outside and could just get the taxi or walk to the office instead of wasting everyone's time, but noooo. He has to climb back to the sewers while the city is falling apart (partly because of him, btw). It's actually crazy. Why are you doing all this??? Just go to the fucking office! You can literally climb over the fence or break the glass door. Instead, you just have to go back underground and waste time doing god knows what. "I don't get paid enough for this shit!!" my brother in Christ, YOU can't get your ass back in the office and prefer to crawl through the sewers. You're in a prison of your own making. And probably smell like shit. The epitome of that is the moment in Chapter 9 when Mark's colleagues just took a helicopter while he was crawling through some trashed and abandoned buildings (once again) and reached the power plant faster (and cleaner). Though the point can be made that he's just THAT bad at his job, always doing anything but what's really necessary. Or that his colleagues really do hate him that much.

And what's with the voice? Sorry, I know it's really subjective, but the guy's voice is fucking obnoxious. Almost uncanny. Even at the start of the game, it feels like everyone talks normally, but he sounds like he just learned to talk yesterday. Or like he's a robot. He is overacting, his emotions sound so fake, and for god's sake, why do you have to make all these comments and "witty" remarks about everything with your annoying voice shuuut the fuuuck uuuup!!!

Why is it so long?

There are obviously thematic reasons for such a slow pace. I guess. It touches on lots of stuff like corruption, the government's and executives' lack of accountability, the divide between white and blue collars, ecology and the importance of proper maintenance. There are moments when you enter a really long hallway, and it becomes obvious that the slowness and tedium are there on purpose. In fact, I kinda like that, it works. But the game is inconsistent in the ways it presents its themes through the gameplay and sometimes the movements and puzzles are just boring, repetitive, or easier solved by trial and error. And there are so many moments that are just dumb. Are you really telling me that the guy who spends hours easily jumping across abandoned facilities cannot climb over the fence or roadblock, swim, survive a 2-meter jump, or just break something? You don't have to be Gordon Freeman to be able to do that. This feels weird considering the number of times he straight-up breaks in and trespasses on someone's property, but I digress.

Why is it so long?

At some point I started thinking, "Is this some kind of office clerk's idea of an adventure?" And kinda yeah, that's exactly what it is. Dungeon crawling, solving puzzles, exploring creepy places, but in real life and as a part of a job. Yet there's still something really strange and frustrating about this game that I can't really put my finger on. It's definitely unique, it doesn't feel like other walking simulators or puzzle games. I wish there was no score to this review because I don't actually hate it. There definitely was a vision and I respect that. It just left me really frustrated. Make of that what you will.

Sometimes a game comes out that implements so many pointless features of a certain era that you start thinking the developers are making this on purpose. Almost everything this game does is makes everything worse by trying to stick all the new shiny things to it instead of just fixing the issues of a pretty good original game. 
Why is it a reboot?
Why does it need a skill tree where half of the skills are the necessary things that were available from the start in the first game and the others are absolutely pointless (the pull object magrope upgrade is the worst offender because all these walls just DON'T EXIST until you get this upgrade)? 
Why can't you get a weapon? God, the combat is one of the worst I've ever seen, the evade/shift movements feel completely random sometimes and often throw you in a completely wrong direction. 
Why making it an open world when you can't even make an interesting open world? Okay, the metroidvania approach is an interesting idea, but the world is empty (and no, in this case you can't say "that's the point!!!").
Why all the pointless collectibles and side quests? Yeah, I know, to make players waste more time on the game.
And worst of all, the movements are still clunky, the shitty post-7th generation "realistic" jumping controls don't fit the parkour/platformer nature of the series, and Fate misses the jump or the right direction more often than she should. And the story and characters are still boring, but now we have more cutscenes because cinematic!! 
The visuals are pretty good, yeah, but while the original game came in the era of piss filter and had a really unique color scheme and design choices, this one is just a futuristic-looking city with various colors. Beautiful, but barely interesting.

Such a based game.
Many games released in 10s tried too hard to do this "this game knows you exist" thing which eventually became so overdone that many good examples of that trope now can only annoy you. However I think The Magic Circle is an exception that stood the test of time, mainly because this "meta" thing serves the narrative purpose and translates the main ideas of the game really well. Bad and arrogant creators drive their games into development hell on the one side and crazy fans and gamers act entitled believing they are owed something on the other. Still relevant today, just as it was in 2015 and years before that. And the gameplay is great, almost forgot how fun the main mechanic is.

Kind of a mixed bag for me. On the one hand it suffers from what every fan-made portal puzzles suffer: they're either too primitive or too overcomplicated. As a result, the game varies between being too simple and being extremely tedious and clunky. The plot is also messy, it relies too much on repeating the Portal 2 formula, but the pacing is completely off, you spend too long in the first act and rush through the other two, and the ending is... yeah. And in terms of originality, though it may be not too honest to ask a fan made mod to reinvent the game but after Portal Reloaded the experience feels lacking.
On the other hand, the voice acting is really fun and well done, I enjoyed the part of the game with Emilia specifically. I also really enjoyed the locations, especially the surface world. It looks really refreshing for a Portal game. Music also fits the game very well and I could easily mistake it for the original Portal soundtracks. And at the end of a day it's still a game with portals and it's hard to ruin that.

This game is such a product of its time. It falls perfectly in this category of late 7th generation AAA games, where everything is gritty and dark and the characters are in dire situations or struggle more than usual. They are very "serious" (because games are serious now), very "cinematic", use all these camera effects, absolutely unnecessary long cutscenes and (of course) QTEs. Max Payne 3, Hitman Absolution, Bioshock Infinite, The Last of Us etc etc. And the problem is that all these games do these things reeeeeally badly and unnecessarily. Long cutscenes work only if the story is interesting and characters are not just action guys (and even then there's time and place for them), the ugly shaky-cam aesthetic peaked in Kane & Lynch 2, and QTEs are shit, oh my God, you don't need them anywhere but in Telltale or Quantic Dream games. But all that aside, the game is pretty good, a bit clunky at times and a bit over the top, but I enjoyed it. Platforming still doesn't really fit this kind of game, but it was alright.

Probably the best indie 3D platformer puzzle first person shooter visual novel game I've played.
The gameplay is amazing, it feels and controls perfectly and the effects especially by the end of the game are just pure fun. It's easy to get the hang of, but it still feels rewarding when you discover some unusual solutions. Level design is insane and despite extremely rapid pace you (almost) never get confused. Visuals are great, soundtrack is great. Everything is filled to the brim with adrenaline, fun and goofiness.
Yeah the writing is cringe sometimes and the characters are cliche, but it doesn't annoy me and even fits the game really well, because it's silly and innocent (like in Night in the Woods and not like in David Cage's games) and full of sincere nostalgia and love for the pop culture. Plus the voice acting is perfect for these characters and the visual novel elements are well executed and sometimes even feel a bit satirical.
Actually the game is full of little nostalgic pieces, all the stuff from 00s games like the ghost playback, prizes in secret places, leaderboards, hub zone, medals, pushing player to replay levels hundreds of times... Parts of the game also remind me of CS surf maps and other parts of more recent Clustertruck.
This is such a fun game and even after completion I want to replay lots of its moments.

It looks great and the concept is cool and it's a shame it was wasted on such an utter shit game. It runs like shit, freezes and crashes every 5-10 minutes (sorry, but if you cant optimize your game you shouldn't even make it), the autosave system is awful and inconvenient (especially considering the crashes), first-person platforming is already a bad concept, but it gets even worse with shitty movement control and excessive difficulty in some parts, which is mostly due to bad game design. Just read BLAME! instead I guess, or hope that someone else makes a better game.