Well, the graphics alone probably wouldn't be worth the money, unless you've got quite a bit of money to be throwing around. If you're planning on getting tons of games, it'll be worth it (Steam sales, ie: everything that Square Enix has published for $75, >$400 savings). Also, mods will extend the lifetime of the games you have, and you can play older games, and there are some games that are legitimately free and good for PC (flash games, and some games like nexuiz
, but that's the only one I can think of). The mouse and keyboard is much, much more accurate than a controller.
In case you're looking for a good GPU to max (about) anything (out right now), I think this
would max about any game you tried with it. I think Crysis Warhead would be able to get about 30 FPS on 1080p on very high with 4xAA, 16xAF. Well, it gets 31 fps on those settings on 1680x1050 resolution.