I miss the days where I can play coop-quake 2 or doom, killing baddies with my buddies. For those of you who reminisce the coop good times without necessarily "connecting" to a server (or team kills) you should give Rainbow 6 Vegas a try.
The single player can be done cooperatively but there is also the "Terrorist Hunt" mode which brings out replayability.
You can have 4 buddies spawn on a map, go around hunting randomly spawned terrorists. The customization of every aspect of your character is also a plus, and has a slight RPG-esque feel.
All in all, if you like killing baddies with buddies on a lan with counterstrike-esque guns (the m4 feels bout the same

) it's a good buy with some replayability.
Now if only they made an oblivion sized game with zelda-esque good fighting engine converted into modern weapons......