Iced your better off borrowing Assassins Creed off a friend, even though it's a good game. It's too repetative, I enjoyed it alot mainly because of graphics and gameplay but if I knew it was this repetative I would have borrowed off a friend crack it then give it back.
Battlefield 2 is a great game, I've had it since release on of the best and only fps games where you have numerous vehicles and weapons you can use.
Crysis is well worth it in my opinion especially for someone with a good gaming rig, Crysis had a goo story line, in fact to good to be honest, I installed the game on a Friday morning 9 am, finished single Player at 9 pm :) Annoying that I finished it too fast and didn't get to enjoy the whole game! So when you play Crysis either put it on a high difficult setting or just take your time and enjoy the game. Well worth it, online is good fun also, but it's best to play online with people you know so you can do some team work since most noobs online just go Rambo and try to win the game themselves.
For racing games, in my opinion GRID is one of the best out at the monemt for PC. Great online game, especially when playing with about 6 of your mater in a 12 man Destrution Derby :D