Basic Differences:
1. Play Minigames over AdHoc Wifi with other players.
2. Trade tracks over AdHoc WiFi with other players.
3. No Speaking from Guests/Mortimer in Tutorial. The UMD size doesn't allow for it.
Otherwise, that's it. Note that if you're use to another version (such as the Xbox 360 or PC version), the graphics are not nearly as nice.