Its not much "better" than the GC version, from a technical standpoint. That being said, I thought it was great. Honestly there aren't many Wii games that can claim to be a lot better than similar GC versions (e.g. Fire Emblem, RE4, Zelda, Paper Mario, even SMG when compared to SMS, really), so I dunno what the heck the mediocre reviews were all whining about.
Its a good game, when judged from what is, IMO, a fair standpoint.