I own 'Beyond Good and Evil' for the PS2, I don't think it's much different on the Gamecube. But I like the game.

Thanks for all the hints. I added Baten Kaitos, Mario Kart, Wind Waker, Killer 7 (sounds interesting), eternal darkness, chibi robo and fire emblem to my list (too much money needed *sigh*). Animals Crossing, Metroid Prime, Resident Evil, Paper mario and Super Smash Brothers will all have versions on the Wii in the not so far future. I think I will try the Wii-version first, and if I like it I will buy the originals for the Gamecube.

About RPG, beware !
Fire Emblem is not a RPG like FF style. It's a tactical RPG, more like all the Final Fantasy Tactics. It's even more different, as there are no random encounters, and the strategy plays even outside battles, where you have to plan the relationships between characters, and how you advance them. Great replay value too, especially since going right from the start in hard mode (where you get the real ending that makes sense, and the real challenge) is unwise. Story great and all, I was sold on this one, as much as with FFT in fact.
Skies of Arcadia Legends is more the "regular" Final Fantasy RPG genre. Quite old with some flaws (lots of random encounters), but a pretty good game. I got it only recently, so have not finished it, but it looks like a killer from the start.
Tales of Symphonia is an Action RPG. A VERY good one, despite we in Europe getting an english dubbed version which is pretty crappy, especially compared to the japanese version. I actually don't like Action RPG (except Seiken Densetsu 2), but this one is really good, with excellent replay value too.

Actually, I think you can't go wrong with any of these if you like J-RPG.

 Paper Mario on the Wii will not be the same as on the GC. On GC it was an RPG lite, on the Wii it's a Jump'n'Run.

So, Baten Kaitos is really that good, should I get the first one or the second one first?

I found this useful. http://cube.ign.com/articles/772/772300p1.html

It is what they think are the top 25 best gamecube games of all time.  They have good explanations and they did it for xbox, ps2, and gba.