I think what is most amazing is that the total concurrent players for League of Legends (5 million) far exceeds the xbox live and psn total concurrent user records. At this rate it won't be long before it passes Steams record (~6 million)... 

SC2 for $20 is a steal.

DoTA 2 hands down, even the esport scene is making the shift. 250k average active users at one time and growing. Production Values and hero balance is much better. You don't need to grind at all, its all down to your skill. Where can you go wrong really?MBirdy88

Agreed. I think what makes Dota 2 very special is that the production is handled by Valve and game balance by Icefrog. It helps that the game has essentially  been balanced since 2003 and the current business model is superb.

[QUOTE="Primordialous"]

DOTA 2

whitey_rolls

Dota 2 is not for the feint hearted but is overwhelmingly rewarding if you get past the intial barrier. It helps if you have some history with RTS.

[QUOTE="Cwagmire21"]

[QUOTE="yellosnolvr"] i see what you mean with WoW and diablo, but i thought sc2 was an exceptional game.Gamesterpheonix

Don't mind him. He hates everything since 2000.

Seconded. SC2 HotS is shaping up very well and Blizz have done an excellent job working with the community.

Warcraft 3. 

Make sure to download SkyUI as the vanilla PC interface is garbage (understatement) unless you plan to play with a controller.

Please refer to the link below. Here you will find a website dedicated to advertising coop games and it has been very helpful for me when looking for new and enjoyable coop games to play.

http://www.co-optimus.com/system/4/pc.html

Personally I would recommend SWAT 4 (underrated series).

Love it. Day one purchase for sure.

Mass Effect - I have tried to get into this game (~15 hours playtime) but I can not bring myself to enjoy it.

GTA IV - Very underwhelming and much less enjoyable than San Andreas.