Games like Assassins Creed, Mass Effect, and Dead space work great with a controller (I use the XBOX 360 controller for my PC). However, you would have a huge disadvantage in MP FPS games such as Black Ops. As for FPS shooters in general, you could pull it off but you'll have to tone down the difficulty a bit.
I tried using my controller once playing Crysis...the results were similar to watching Richard Simmons working out in spandex, which is to say atrocious!