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?

I can understand your points about why the ending didn't land with you, but personally I found the ending super emotionally resonant.
One of my favourite aspects of the game is how insignificant you are in the setting; this isn't a story where you can be a big hero and change anything of real note — Revachol (and Martinaise especially) is haunted by its past. Communism is a part of that past, and so discovering the killer's identity felt like a logical consequence of the world in a way, even if it was super out of left field.
I agree with you about the yuck about the weird sexual fixation the shooter had, but I liked what that did for his character and the story. Like sure, he's a vehement communist, but he's also a deserter who is an asshole even if you're playing as a communist. It also seems like Evrart knew of his existence and even used him to do a political assassination previously. I like how this makes the world feel messy and fundamentally human. Ideological questions are important, but we can't have grand debates about capitalism Vs communism without reckoning with the messy reality of the humans who are advocating for those ideologies. The deserter became fucked up because he has been tremendously socially isolated, and he lived that way because he lived in a time when they were lining up Communists against the wall to execute them. He is a toxic loser, and in that way, he represents a tragic culmination of the fucked up world of the game.
Along similar lines, I liked that characters like Klaasje didn't end up being related to the mystery of the killer. Her lack of greater narrative significance helped me to appreciate the nuances of her character, rather than her just seeming like a plot prop. For example, the weird relationship she has with Lely is hella fucked up: she knows that he has killed and raped civilians. She knows he is a piece of shit, but also, she seems to see herself in that light too. If she is disgusted by him, then sleeping with him may feel like a sort of "punishment", or self harm. That's speculation, but certainly it seems like their relationship was pretty toxic. I think she does say something about how they deserved each other. Part of her depression seems to be linked to the lack of her significance in the world. After all, she had pissed off some people enough that she was having to hide out in a shit hole like Martinaise, a place that the world had forgotten. It seems pretty likely that she was a spy that was working for some corrupt people, and those people probably would be anti-union, and that feels significant, even if this is only true in a far more general manner than what you were speaking about. Ultimately, the true conflict of the game is one that transcends the murder of one mercenary, or the striking of one union, or the escape of one corporate spy. It's the question of "the world is fucked — what do we do about it?". Klaasje is burnt out and hopeless because she doesn't have an answer to that question beyond striving for her own survival. Klaasje doesn't matter to the story, and she knows it.
Kim took a photo of the phasmid in my play through. Did that not happen in yours?
Regarding the prospect of explaining the phasmid's existence, I think it's possible. It could just be a large insectoid creature that secretes hallucinogenic pheromones, and the conversation that Harry has with it could be hallucinated, even if the phasmid isn't. But also, when considering the phasmid, we should remember that the pale is an established part of the metaphysics of the world, and that entroponetics is a field of scientific study in the world of Disco Elysium. That is to say that it may be scientifically explainable in world. I enjoy the ambiguity around it though. I share your disappointment at not seeing the cryptozoologists reactions to the photo, but also I suspect that I would have been more disappointed had I been indulged here, if the scene hadn't been as satisfying as how it would've gone in my head. The phasmid is a weird as hell element, but for me, it ties up many of the themes in the game, like the idea that there isn't a Plot to the world, and that "reality" is just a dizzying network of connections between people, places and ideas. Like, the notion that the phasmid's hallucinogenic pheromones may have contributed to the deserter's cognitive decline and psychosexual fixation on Klaasje is utterly absurd, but somehow (for me, at least), it doesn't feel contrived — the absurdism is the point.
Regarding the final conversation with your colleagues, I found that a satisfying conclusion, but that may be because it felt like an appropriate ending for my Harry. It was a bit of an anticlimax, but I wouldn't have it any other way. After all, the world is still fucked, and even if you've played Harry as someone who is on a path to recovery, any hope in the ending is bittersweet. I like the vibe of the thought cabinet perk from going sober:
I haven't struggled with alcoholism myself, but this framing of recovery was something I resonated with. Sometimes, I find myself feeling wistful for times when I was more severely depressed and grappling with suicidal feelings, because back then, I thought of it like a grand battle between life and death. Well I chose life, and the hardest part is that I need to keep choosing life each day (and also that "choosing life" mostly entails mundane tasks like dragging myself out of bed each day (especially when I don't want to)). It's an odd feeling: distinctly hollow, and yet there is a small seed of hope that has the potential to grow to fill that empty space.
Harry's ending feels similar to my own, in that it isn't an ending. Some things can improve, like how Kim going to work at the 41st precinct is definitely a positive thing for Harry, and showing Lena the phasmid would undoubtedly buoy his mood. And hell, maybe it'll be positive if Harry returns to work, but doesn't lead the squad anymore — maybe it'll be less pressure. But despite these concrete improvements, it's not enough to negate the gargantuan effort it is to exist in the world as a fucked up person (especially in a job that puts Harry right up against the world's suffering). In my ending, Jean Vicquemare seems glad that Harry's achievements will mean they probably won't have to fire him, but that too is bittersweet because he's also someone who is fucked up in his own way. I wish that we got a "better" ending, because I want the story to end in a nice, resolved manner for these characters, but that wouldn't be realistic. In a sense, my frustration and wistfulness is the core theme of the ending, and if I let myself sit with those emotions a while, I find them giving way to a tentative hope. Similarly, right now, I feel frustrated at the arduous task of needing to get up and make food (I am emotionally tired, and it feels excessive that we have to do this every day), and I am hurting due to chronic illness and I wish that things were different because this isn't fair. If I let myself feel all that though, I remember that I am here because I chose to be. It's bloody difficult, and there's so much awfulness in the world that makes me feel small, but there is so much good that I care about that gives me strength on the hard days. I'm never going to change the world, or be anyone of note really, but by focussing on what is worth fighting for, I can be a part of something larger than myself. For me, the ending of Disco Elysium captures this complex blob of emotions.
The Deserter is an image of what Harry will become if he does not change, so for him to be hung up on a woman felt completely natural narratively to me and perfectly appropriate for him in his role as the Ghost of Christmas Future.
I'm still processing all these new perspectives I'm gaining reading the comments in this thread, including yours, so I don't have anything thoughtful to add right now. I appreciate your perspective and thoughts on this. And thank you for sharing your personal experiences - that's not a given.
I hope you're better nowadays 💜