Some folks in the Arstechnica forums have done direct screenshot comparisons of the 360 and PC versions of Prey (using some fairly high end PC hardware). The 360 fares a whole lot better than I expected. Sure the PC has a few better features like anisotropic filtering, but the Xbox 360 version is getting fairly close. Add in that you can sit on your couch and play it on your huge TV, and it looks like the choice between 360 and PC versions of some games just got tougher (unless you find that playing FPS games with a controller is pain in the rear, like I do).
[url=http://arstechnica.com/journals/thumbs.ars/2006/7/5/4528]Direct comparison of Prey’s graphics on the PC and 360[/url] (Arstechnica)