If you have a fast computer and want to see the eye candy it's capable of, Need for Speed Hot Pursuit is an excellent racing game to try. For shooters, Crysis 2 is beautiful or even Unreal Tournament 3 (although it's been out a few years it still looks amazing). Mass Effect series, Assassin's Creed series and Modern Warfare/Black Ops also of course. I got bored of Mass Effect 1 half way through but that provided enough introduction to the Mass Effect universe that I knew what was going on in 2 and 3 (which were much better, 2 especially).