I thoroughly loved the Gamecube. Then again, I may be a bit biased because it was my first console system. But come on, it had great games. Wind Waker, Melee, Tales of Symphonia (yes I realize there was a JP PS2 port but my box still says 'only on gamecube', darn it!) Zoids: Battle Legends (but then again, I'm a Zoids nut) Baten Kaitos and Baten Kaitos: Origins.
I think the main problem with the GC though (and to an extent Nintendo in general) is that they've never had stellar 3rd party support. There's been gems amid the sea of mediocrity but Nintendo's systems mostly stand on Nintendo's games. And if you don't like Nintendo's games, you tend not to like their systems.