I really wish i could play fun cooperative games. As far as my experience goes, the best of the best i played in that sense was SWAT 3 Elite Edition.

That (version of the) game came with coop as one of the options, and it worked just fine. Add to that the fact that the computer animated bots (the terrorists/punks/bad persons) were quite credible in their behaviours and good graphics (specially when played on a screen projector: it looked like you weer in an action movie) and it was a game that me and a couple of friends played for nights and nights.