You guys should definitely try Day of Defeat: Source. For those of you unfamiliar with it, it's a team-based (and class-based) WWII shooter based on capturing and controlling all points on a map simultaneously to earn victory. Scores aren't calculated in kills or k/d ratios, but in point captures. The frenetic action is somewhere between Counter-Strike: Source and Team Fortress 2. Plenty of nice and moderated servers, quick respawn waves so you can get back into the action quickly. IMHO, more casual than Counter-Strike: Source, but more hardcore than Team Fortress 2. Might take awhile to get used to the ballistics and weapon handling though.
Here's the server scoreboard when I lost my connection after a hard day's sharpshooting (4 Captures/325 Kills/185 Deaths):

"There is no teacher but the enemy. No one but the enemy will tell you what the enemy is going to do...Only the enemy shows you where you are weak. Only the enemy tells you where he is strong." - Mazer Rackham