Single-player, the Fallout games are excellent, and the VATS combat system adds a dimension to the FPS aspect.
Multiplayer, BC2 is a love/hate thing I think. To me, it's like listening to U2 - I can see what makes it good, and understand why so many people like it, but I have decided that it's cack. Too much like hard work, not enough fun.
So I'd say give MW2 or Black Ops a go.