Not necessarily in this order:

Halo - A silly wanna be FPS that couldnt be anymore simplistic.

Guild Wars - WTF is this game anyway???

Grand Theft Auto (any of em) - Can I do something OTHER then shoot people and steal cars?  Guess not...

Metal Gear (any of em) - Still have no idea what is so good about this franchise...

Any WWII themed FPS/RTS or whatever - I think one was enough...