Holy doly, where to begin?
My co-op experience with D:OS 2 was riddled with bugs. The ones I ran into ruined my experience to the point that my friend and I quit the game just before the end of chapter 3.
So let's start a list.
1) Disconnects after saving. This happened about 1/3 to 1/2 the time. Basically I lost my connection to host (my friend) when he saved. He'd invite me back afterward and then I'd load in. This ended up happening probably a few dozen times over the course of one co-op playthrough.
This is unique to D:OS 2. It doesn't happen for me in any other game, and it didn't happen in the first D:OS either. It seems to be more of a syncing issue (?) Even the most recent patches haven't fixed it.
2) Skills do not properly connect.
Exactly as it says. You'll wind up for a skill, have perfectly clear sight to the target etc. and for whatever reason the skill never lands. I've seen bouncing shields disappear into thin air, poison darts vanish mid-flight and other inexplicable happenings. Why? The game doesn't say.
This one's less frequent but it still happened a dozen or so times.
3) The game lies to you about being able/not being able to perform a skill.
I'm pretty sure this a holdover bug from the first game. You can often perform skills or attacks which the game says should be impossible. It's wrong about 50% of the time.
4) The RNG's questionable (or it at least appears that way).
I've seen more 95% chance to hit misses in this game than almost any other in the past ten years. I'm not sure if this is actually bugged, but it might be helped by pseudo-random distribution.
5) Enemies can move into spots on the same plane where they cannot be targeted by melee.
A certain key fight in the sawmill had one ranger ducking behind a mirror next to a bed. He couldn't be hit by any melee attacker despite a lack of height difference.
6) Bone widow in general.
You can spawn the bone widow close enough to enemies to the point that it can't attack. Seems to have something to do with its size.
7) Corrupted saves.
Happened once or twice near the middle of chapter 3. Had to replay another key fight. [i]Sigh.[/i]
8) Couldn't end turns near end of chapter 3.
The game just up and stopped responding near the end of a tough fight. This is where we quit after all the other issues kept piling up. [i]Baby, it got old.[/i]
All in all, this is one of the buggiest games I've played in a long time. I'm shocked more people haven't run into these problems. It's worse than in the first game by quite a margin, and ultimately I don't feel D:OS 2 was worth the asking price. Co-op was a rough experience.
I'm disappointed. I distinctly got the impression that Larian has given the short shrift to co-op in favor of single-player presentation.