I have owned a Wii for some time and then I got a 360. The first thing I noticed is how it doesn't look nearly half as good as people claim it does. It's probably be because I have a SD tv but the only games I find really good looking are Halo 3 and Assassin's Creed (well, from what I played). There are games that just look ugly. Soul Calibur IV look worse than Soul Calibur 3 on the PS2.
My conclusion: if you don't have a HD TV, the Xbox 360 graphics don't look that good.
How many cups of darkness have I drank over the years? Even I don't know...