I mean, I get that you like it, but I'm a little surprised you wouldn't get the hate for the game. It's gloomy, as you say.
If you'd like a few other reasons, I can throw some out there:
-Many could never stomach the idea of playing as Abby. They tried to make her and her circle of misfits more likable than the vengeful Ellie with the puppies and the pregnancies and the whatnot, but many found it hollow and sided with Ellie regardless. That make playing as Abby a chore.
-I believe someone called the game misery porn above. While the first game could definitely be dark, it had enjoyable elements. This was just a miserable slog, and lots of people don't like that.
-Finally, from a storytelling perspective, Druckmann made the mistake of constructing the story around themes rather than characters. This is a usually a hallmark of shallow, pretentious storytellers and, as a result, their story does in fact convey their theme, but only on a surface level. TLOU 1, on the other hand, was a character-driven game that was pretty well-liked by everyone. The sequel was greatly missing Amy Hennig, who wrote most of part 1 and was jettisoned by Druckmann for being better than him at everything. (Joking. Maybe.)
The consequence of theme-based storytelling is that the characters are often a square peg that needs to fit a round hole so that everything serves the theme. The problem is compounded if the characters have a history and defined personalities and motives. You now have to sometimes contradict those to get your theme across.
So the tl;dr
1) Lots didn't want to play as Abby for spoilery reasons
2) Misery porn
3) Superficial/Shallow storytelling