We've recently finished our first playthrough, and I must say: I'm a little disappointed. Heavy spoilers for the ending of the game, so be aware of that when reading here.
I found the reveal of the true killer kind of annoying. It's a completely random person we've not seen throughout the game yet, so there was no way of us putting pieces of information together to form a theory - it's a completely unrelated person. In addition, I didn't like the motivation he had for killing the mercenary. Sure, he's a veteran of the former revolution, he despises everything that's not communist and took a problem with a mercenary having a sexual relation with a woman he spied on for months. But that whole parasocial sexual relation, the peeping, the ultimate motivation for the killing... I don't know, kinda yucks me out and didn't feel compelling at all.
Imagine if, after the tribunal, Klaasje's disappearance was related to her actually being the killer. That would have made sense. But she was likely just afraid of how he leads would make her look like the prime suspect, so she fled. Still, I probably would have preferred her to be the killer somehow. Some kind of spy/agent working for some corrupt people who want smash the union or something.
Then the whole thing with Ruby. It was an intense encounter finding her under that ruined factory and the confrontation was quite dangerous - we almost died there. But her ultimately not being related to the killing at all apart from staging the lynching was also just kinda annoying. I get that we didn't have any other leads that made sense at the time so Ruby was the only logical suspect. But her just completely vanishing after our realising that she's not the killer felt anticlimactic.
Then the encounter with the phasmid. It was cool, I guess, but ultimately, it didn't really contribute a lot to the story, I feel like. It's insinuated that the Deserter was somehow aware of its presence on his solitary stay on the island, but you don't know for sure if he actually saw it. Who knows - maybe both Harry and Kim hallucinated. There is nothing scientifical that would explain the phasmid's existence. But even putting all of that aside, it was a little disappointing to me that you don't even see the reactions of the cryptozoologists. Felt a little robbed of that.
Then there was the ending itself. After finding out who the killer is, I was 100% sure that the game wasn't finished yet. The huge climax when you are confronted by your former colleagues felt similarly intense to the tribunal itself, and I was sure that this would lead to further development in the story. But nope. It's over, just like that. I feel like something was missing there, but I can't quite put my finger on it.
So yea, my unfiltered thoughts I had on this. It's still an amazing game and I'd really like to make another playthrough. But the ending did kinda suck to me. I've read a bit of discussion on the ending online and some points felt valid but didn't change my mind too much, overall.
Thoughts?

It also needs to be said that the game has an absolute fuckton of missable content that is absolutely crucial to picking up the point of what the writers are trying to say. Disco Elysium really is just like they wrote a book, scattered the pages across a room, and then put blind faith in the player finding all the important ones on their own.
Like, I've seen so many people completely miss the Final Dream just because they didn't want to take a nap in the flak tower. That scene with "Dolores Dei" is like, the denouement of the entire game. And the devs made it so easily missable. Completely psychotic behaviour, hah.