Yes Slowbieone, you can play through the heretic 2 single player missions co-operatively. Which i did, and which was very fun indeed, and added a lot of life to the game.
Co-op has sought of gone out of fashion with the multitude of mindless, instant action deathmatch games. Ok some of them are great like CS. But CS introduces co-operative teamplay, which is one of the reasons its so successful.
I'd personally love to see co-op in jk2!
No way, man. No way, man! Get yourself another patsy, man. No way am I wearing a freakin' wire!