I really liked the GameCube - it was a great console with tons of awesome games. I especially like the controllers, which are among the most comfortable ever. 3rd party support was actually pretty good - there were good versions of many big franchises. Lots of quirky and cool exclusives, though I think Nintendo's game quality started to decline a bit.

Two dings:
1) The first set of memory cards were really small - you didn't have enough space on a card to save a Madden franchise, for example, until larger cards came out later.
2) The smaller capacity discs meant games often had to cut corners (compress audio, etc).

Overall, though, I really liked the console.