So yesterday my friend and I tried our first session of coop. We had bought this game specifically upon hearing coop was possible and decided we wouldnt play ahead without each other so that it would be the first playthrough for both of us.
So how was it:
1) Coop combat works really fine.
2) Be careful to not run around seperately even with just and trigger encounters without the other player being nearby, even being 20m behind is quite a distance to cover in combat.
3) When running around talking to people seperately it can get kinda weird - I was suddenly teleported from a conversation to another location (the imp and library place) without having a clue what was happening
To sum up - Coop combat is great !

Investigation, Following the story and having a clue whats actually happens in coop is pretty damn hard ... so I probably wouldnt recommend coop for my first playthrough like we tried and to be honest Im not sure I really think coop will ever work well in a game with this ratio of action to non-action (investigation, shopping, crafting etc.)
Now it should be said, I did have coop recommended to me by another friend who says its all 'great' ...so what do I know?! Whats your guys experiences so far?