Finished it just now. TL;DR version of the post below: It was pretty damn good, but not as good as I'd hoped. Spoilers for all of Alternative, naturally.
First off, since I just went through it I guess I'll talk about the final mission and ending. I must say, I found the buildup of Operation Cherry Blossom to be quite superbly made, and the operation itself did live up to that. My main problem comes with the last stages of the operation and the subsequent ending. Sorry, but having the protagonist's growth and overcoming his weaknesses be pretty much the main focus of THE ENTIRE SECOND THIRD of the story and then having him nowhere near over those weaknesses in the last mission to the point where all the other characters purposefully deceive him so he doesn't compromise the mission because of it... was not nice to see. Especially with how Meiya's death scene was stretched out to I think almost ten minutes. If that scene had instead been Takeru making up his mind and just shooting immediatly, that would've been a great way to show how far he had come. I feel that really was a missed opportunity. I guess he'll never really change after all. I still have no idea how the Susano'o suddenly got all its sapped power back to make that last shot btw.
As for the whole causality conductor thing... eh. I didn't care for the final explanation. Maybe it's because I never got an explanation for how the space-time continuum got ripped that satisfied me. Maybe it's because I expected an explanation that just clicks all the pieces together for an ultimate "oh shit" epiphany. Maybe it's because I had hoped it would include an explanation for the BETA's existence in that world beyond "they came from somewhere for some reason." But mostly I think it's because it just felt kinda handwaved. Like yeah, okay, Sumika was able to do that. It happened. Uh huh. Oh well. I guess I'm spoiled from other VNs when it comes to great explanations for the multiple worlds plot point.
Final Episode MuvLuv was a bit too short for my taste. No idea how that world came to be, no idea where it's headed. I also really, really wished for Takeru to just retain all his memories. So to me, that was not the best way to end the story. Also a bit disappointed in the lack of a Music Room.
But all that negativity aside, MLA was great. Atmospherically it was incredible, building a world with such a well-conveyed feeling of desperation and immersing the reader in it completely. It has by far the best-looking action scenes I've ever seen in a visual novel, and it was really good at making dramatic war and battle scenes. And yet, the chapter where Takeru returns to the Extra-world is probably my overall favorite part of the entire VN because it's really gripping and makes you so badly want to find out what's going on and how to stop it (too freaking bad it never got a proper satisfying explanation, but I've gone on about that long enough). That freak accident of Sumika's was total coincidence, wasn't it? ...anyways. One thing MLA did wonderfully was to make the 'fun times' of Extra feel nostalgic and make you invested in having Takeru get back to them. Takeru x Sumika was my OTP since forever so seeing it be the main focus was quite satisfying. Poor Extra-Meiya though. Besides that, the entire scene with Beta-Sumika's backstory was so damn well made as it simultaneously shocked me and made my immediate respect for Takeru for his reaction shoot through the roof. Finally, the OST and opening movie are amazing. The best I've seen in quite a while.
So in the end, what can I say? I enjoyed it for sure. It was a great read. But did it live up to the hype? No, definitely not. I suppose my final impression was hindered by the high expectations I had of the story's integrity, which reaaaally isn't one of MLA's good points. It takes liberties that I was dying to hear an explanation for but never got one that actually satisfied me. And it's not trivial details that went unexplained, it's parts of the plot I was actually very invested in, which is why it bothers me as much as it does. The cast of characters was great, but not that outstanding either. Especially when it comes to development there was a lot to be desired. Don't get me wrong, there was quite an amount of good character development... but there was the potential for so much more than that. And that's how I feel about much of MLA, and the entire thing as a whole as well. Great, but with some improvements it easily could've been unforgettable.
Well that's that. And with that I've finished my must-read list of visual novels. It was a busy three months.
Edit: I didn't go back and choose any different choices yet. Should I?