If you picked up Painkiller: Resurrection on the PC last week with hopes of glorious cooperative stake gunning in your head, you may have been disappointed to find no menu option for co-op. Rest assured though, the game does have co-op support, it's just a little ridiculous as to how you have to start it.
"To play a coop game you have to start a dedicated server with the tool provided together with your game. Pull in the campaign maps from C9L01 to C9L06, choose FFA and start the game. You can also add / remove bots accompanying you there. We will add a more convenient ingame coop menu with the next update "
That's from a JoWood representative on the official message boards. Were you expecting a nice simple solution for co-op? Sorry, none to be found here. Thankfully JoWood confirms they are working on a "more convenient way of accessing co-op" in a future update.