Doom3 on the Xbox does not equate to the same experience on the PC. Graphic wise. None of the 3d shooters do, but they are STILL excellent quality. Expecially the games that support higher HDTV resolutions. Playing it on the xbox is like tweaking the game down to get a higher FPS, making it a little less "edgy" for speed. But damn they look good on the tele. Oh plus you miss out on some of the fancier special effects. Since the game is specifically designed and tested on fairly consistent hardware, it's tweaked to perfection for the device. They aren't just ported over and the one's that are simply ported are CRAP.

Xbox definitely has a place in the houshold.

//EDIT

BTW: many of the HD screens are only capable of 1280 x 768 yet to see (in OZ) specs above this. Seeing as this corresponds with the 720p (why would you want 1080i - or only 540 vertical lines of resolution)
That 720p (progressive scan) is in 16:9 aspect ratio. The key here is progressive scan. 1080i as you can tell from the "i" for interlaced displays 1920 x 1080 pixels across the screen in 16:9 aspect. HDTV support 1920 x 1080 in the US in fact there are a few channels that broadcast it. One might think, shoot 1920 is best why doesn't everyone use that? It's too detailed and looks like a LCD when your playing doom3. You get artifacts but there are channels like PBS that go with it. When you buy a TV you muse MAKE SURE it supports both, if you want to use them or at least make sure it can convert the native 1080i to 720p for display. Most tuners or satelite systems let you set the output resolution as well, so you could get a cheaper TV and still have cool ass vid.