Gamecube is a lost gem almost on a par with the Dreamcast, I had a Panasonic Q for a few years before scaling back to standard Cube, great piece of kit. Oh and near instant load times, going from a Cube to a PS2 is a huge culture shock in that department.
I have to make a stand against the childish comment though, yes there are more than enough games to keep the kids happy but this little lot are pretty involving even for the older folks...
Probably the best versions of the Resident Evil series you will ever play, Ikaruga (the hardest game I've ever played), Phantasy Star, Metroid Prime, Castle of Shikigami II, Tales of Symphonia, Eternal Darkness, Zelda: Wind Waker, Viewful Joe etc. And I imported one of the best fighting games I've played, Naruto: Gekitou Ninja Taisen 4. The thing with many is that they are (or were) Gamecube exclusives.
But thinking about it the most fun I've had playing games has been on the "childish" games, Animal Crossing, Donkey Konga, Super Monkey Ball, Pikmin etc, childish = good fun, whch is what its all about!