Again, it seems like I see this kind of thread all the time. OF COURSE IT'S WORTH BUYING (as someone said, this IS a GCN forum, after all...haha)! That said, nearly any system is "worth buying" if you have the cash.
The GameCube doesn't boast huge 3rd party support, but games like (I need to just save this list for pasting, people ask about it so much) Super Mario Sunshine (much maligned, sadly, but really quite brilliant 99% of the time) and Metroid Prime (which any CUBE owner MUST buy, regardless of what you think about it--because you'll be wrong if you think you don't like "that sort of game" more than likely--it's that surprising) make the system worth purchasing, but then you have Pikmin, Super Smash Bros. Melee, Wave Race, Rogue Squadron, Eternal Darkness, the Resident Evil games, Animal Crossing, Super Monkey Ball 1 and 2, and on and on. And those are JUST THE EXCLUSIVES. All must-buys, with the exception of Wave Race, possibly. Now, factor in all the other 3rd party games that are exclusive or multi-plat, and you've got yourself a good little system.
This has all been said before, elsewhere, so forgive me for reiterating.