I would say Mass Effect over GOW. I have both and I know which one hooked me with the better storytelling.
Not saying that GOW is bad though, I thoroughly enjoy a co-op session every now and then. But seriously Epic: not every marine has a gravel voice and not every black man is MC Hammer. Some variety there would be nice please.
Bioshock has a very nice story, but it takes a while to get into, and I still think Mass Effect's was better realized, for one it doesn't have the problem where every character looks like it was made by a small child out of plasticene. I did like how there was little difference psychologically between the NPCs and the "zombies" though, a nice touch there. Assassin's creed is best-played on a console, IMO, the controls just feel better that way. Crysis is good if your PC can handle it, just don't expect any plot twists that aren't telegraphed by about a mile.
COD4 definitely but if you haven't got the Orange Box yet then I doubt your taste in games is good enough to enjoy any of the above
And after that somewhat fevered exposition, I shall collapse now.
Px Out.