Two things that seem to be becoming common in games are (1) online play, and (2) co-op, though the latter seems to show up more on console games than PC titles. What surprises me though is the apparent dearth of games which combine the two - what’s the last non-MMO-and/or-RPG game you heard of that had more than just token co-op gameplay? (No, the Invasion game type on Unreal Tournament 2k4 doesn’t count.) The only one that immediately comes to mind is Left 4 Dead - yet it’s been a smash hit, so it’s odd that more games aren’t following in its footsteps.
MMORPGs (and MMOs in general) have been all the rage lately, but sometimes you don’t want to muck around on an entire realm full of other people - sometimes, you just want to hang out with your friends in a private game and play. Of course, plenty of non-MMO games offer competitive modes for networked play, but it seems that very few offer the ability to play cooperatively with friends over the internet.
Maybe this is just a matter of impressions - it’s quite possible that you all might point out plenty of examples of how I’m wrong. Honestly, I hope you will, because co-op play is something that I miss dearly at times.