Includes comparisons with the PS2 version!
Soul Calibur 2 for the GameCube is easily a better-than-the-arcade port. There are mountains of extras: a handful of new characters, new stages, all sorts of different survival moves, the Weapon Master mode, and the list goes on.
The graphics easily look better than the arcade version, but that might just be because it doesn't have a scan-line-riddled monitor like most of the arcade units do.
Link is fun to play with; he's fast and most of his moves are easy to perform. He can pull lots of fake-outs by swapping weapons quickly, and can take potshots at guys from across the screen with his arrows (although they are easy to sidestep).
Necrid is more awesome than he looks. He automatically generates an energy weapon for each move, and he seems to have borrowed a few moves from everyone. For example, he can do Maxi's back flip kick, and use Nightmare's dropkick to hit them mid-air in a combo.
Weapon Master mode has pages and pages and pages of story and instructions. Too bad it's all in Japanese. It usually isn’t too hard to guess what you're supposed to do, but it is a serious downer to miss all the pages and pages of story. If you really care about this, consider waiting for the US version. One neat feature of the Weapon Master mode is the dungeon-type areas, where you choose which room to move to next - sort of like exploring a dungeon map in the original Legend of Zelda. Also, the first few unlocks come FAST from Weapon Master mode. You'll have some new playable characters in 15 minutes, seriously.
Compared to the GC version, the PS2 version has slight color bleeding and some slowdown when there are a bunch of menus on screen. No huge differences, though. Heihachi is surprisingly fun to play as, and it's too bad the GC folks don't get him too.
A few of my friends complained that the GameCube controller is ill-suited to SC2, and they may be right. It's tough to hit pairs of buttons like B and Y or Z. You can set shoulder buttons to be pairs of buttons, but who cares when you have an X-Arcade, right? The X-Arcade is ideal for this game, so that may be worth checking out if you know you're getting SC2.