It all boils down to taste at the end of the day, but I would almost definately consider Star Fox Adventures and Metroid Prime (though I have read your concerns about the game
)...
Oh, and this is 99.9% unlikely, but I think last time I checked IGN's release list, it said Mafia was coming out end of 2002, the game tha is very similar to GTA 3, but bigger and better. It's funny though, I haven't really heard much about the GCN version, so maybe it isn't coming...
There is also RE 0, and BG
A (if you haven't purchased it for the PS2)...
Edit: Oh, I myself would get Timesplitters 2, and even though it is coming out for all three consoles, apparently (said most of the editors at IGN) the Gc version controls the best. So if you can't get it for PS2, get it for the GC.