Drop Harry Potter and add Resident Evil Zero to that list and I'd be in 100% agreement... with the list of best-looking cube games, anyway. I owned all four consoles from last gen and, truth be told, Xbox did outshine the Cube in a few games. Specifically; Chronicles of Riddick, Doom 3, Burnout 3, Jade Empire, Oddworld Strangers Wrath... there's others, but that'll do for now.
For games brought out on multiple platforms the differences obviously varied from game to game. Gamecube got a lot of bad ports but there were also some games that I thought were best on the cube. Often this boiled down to Xbox and Gamecube games looking virtually identical but the cube having quicker load times (I'm thinking of Beyond Good and Evil, Prince of Persia, etc). Timesplitters 2 looked identical on both platforms; as far as I could tell the only difference was that the Xbox version had more memory for the map editor. Most FPS I bought were for Xbox but that was mainly because it had a better controller for shooters than the Cube (IMO).