I'm sorry but the Xbox was without a doubt the most powerful and it showed. Although GC could put really beautiful games it couldn't handle the best Xbox could offer. Framerates was better and jaggies were less apparent on Xbox. Also there was some particles effects not possible on other platforms and some blur effects. Everything was so smooth and like someone said they could output at a higher resolution.
Only on Xbox could you get graphics like these
Project Gotham 2
Rallisports Challenge 2
Black
Ninja Gaiden Black
Kakuto Chojin
Conquer Live and Reloaded
Chronicles of Riddick
Some of the geometry on Xbox games weren't even possible on other platforms, games like Splinter Cell Chaos Theory had landscapes different from both GC and PS2 because they weren't powerful enough. Some lightning found in games like Doom, SC, Riddick couldn't be found in competitors games. Every multiplat games were far better on Xbox. There were impressive games like F-Zero GX on GC but nothing that could surpass the best Xbox had to offer... damn I even remember games like Burnout 4 which were simply stunning (IGN gave a better graphic score for the PS2 version simply because it was impressive for a PS2 title eventhough it wasn't on par with the Xbox version).
