Just had a coop playthrough with some random server, only one other lad was inside it and we play all the way to the finish, no gameovers thankfully.
Didn't use the chat, just gestures and voice commands.
Kept randomly getting kicked out of the server due to some overflow thing, but overall pretty fun.
But then i was thinking, is coop like an afterthought to the mod?
I've seen videos of people playing coop and they either kept getting wiped with barely any ammo (especially in the lake) or got themselves stuck fighting the noclipping trigger_hurt chainsawers.
Of course, it could be because they played coop first instead of SP first, but if that's the case, shouldn't there be a warning for that?
Besides the Chapter 9 thing, some people are daft and would probably think that was a glitch.