My current preference for games are the following:
World of Warcraft
Planetside
Call of Duty: Modern Warfare 2
I bounce between these games a lot, and finally got a chance to play Halo 2 now that I went to Win 7. I also played Starcraft 2, but not on a multiplayer level cause I know I get my butt trounced by queuing RTS people.
My only gripe right now is the problem with hacking going on with games like Planetside and MW2 where it is darn obvious seeing people violating the rules of the game and not much we can do about it, especially in MW2. In Planetside, it is hard to get an admin to catch hackers, but what seems to be a prevailing problem is just simply how a lot of hackers are now creating polymorphic hacking programs and will probably still be running on XP or Vista to still take advantage of things that you could probably patch and prevent from happening in Windows 7.
For me, I tend to enjoy the MMO type games, but so far WoW has held my interest due to the people, haven't gotten into the other games and find some MP games fun, but rather... Limiting in space. Planetside, being well over 5 years old, is still fun for me not so much the lack of most 'instant death' scenarios like in most FPS, but having the largest Combined arms warfare that doesn't make the control sets so frigginly impossible to play like in Battlefield.