I'm getting fed up with l4d, and BC2 is still broken. So I'm looking for a good team based game to play online, preferably with smaller teams, larger games just become a disorganised mess and are no fun
I second Killing Floor, and I'd also like to suggest Borderlands? Great game and I've got quite a lot of hours out of it.
Fun by yourself, much much better with friends.
Borderlands is quite limited though. You can't just pick it up and want to play it occasionally, you need a party of upto 4 people who are willing to play together often since even 1 or 2 levels difference in the party if they played alone or without a member screws the balance of the game up.
I would completely disagree there, I played it fairly casually with the friends that I played it with, and the difference in levels was often more than one or two levels as well, and it didn't present us with many problems or issues.
The friends I play with often played alone as did I.