League of Legends is team based competitive multiplayer sorta Diablo-esque. Torchlight is basically Diablo. LoL isn't officially on Mac but supposedly plenty are running it anyway. Borderlands 2 only gets harder with buddies so you'll have backup but the enemies are harder and stronger. Who knows if that'll get a Mac release. But yeah, I got a ton of other games.

I see, as long as my desktop is on I'm logged on Steam, mostly to keep social channels open. I play a lot of co-op games with my old friend Mike so if we share any common games I'll totally play with you. Right now, in terms of co-opable games, I'm frequenting League of Legends, Borderlands 2 (a gift), and sometimes Torchlight 2. I'm not into Minecraft though.