The 360 is based on the Nvidia 7600 GT.
Heres how it compares to modern video cards.
Notice that the chart is for common video cards.. it does not include current top end cards such as the Geforce GTX Titan, which scored 8215 - making the best PC GPU 43 times better in performance. Now bare in mind that you can actually put 3 Titans in your machine if you choose too!
PC gaming is held back by consoles, every game that is made is made with a console in mind, so producers never really get the chance to fully test the PC's capabilities. It's financial of course, only a small percentage of gamers have top end PC's so making an exclusive top-end PC game is out of the question...but if they did... console owners would shit themselves, they'd never be able to look at their consoles in the same light again.
If everybody had PC's instead of consoles, we'd probably be playing photo-realistic games by now.