From what I've noticed...
- The title screen is different (old logo, ESRB logo etc...),
- There are no gameplay options, it takes you straight to a character then cup select screens,
- 8 characters to choose from,
- Either Nitro or Retro Cup,
- Nitro includes Figure-8, Yoshi Falls, Cheep Cheep beach, Luigi's Mansion,
- Retro includes SNES Mario Circuit 1, N64 Moo Moo farm, GBA Peach Circuit, GCN Luigi Circuit,
- Some music is slightly different (figure-8 circuit for ex.),
- A lot of graphics are different,
- Some tracks look slightly different (cheep cheep beach has grassy verges that aren't in the final build),
- The map screen looks slightly odd and the character icons and fonts are different,
- Bullet Bill isn't in the game, but the Chain Chomp item is,
- The results screen and the trophy screen look different.