The graphics in the game look extremely nice, rendering 3D models into graphics that fit just right (Donkey Kong Country!) for the GBA. The sounds and music in the game are also decent. However, the gameplay is severely lacking.
When you are pitted in a boxing match, you're doing nothing but moving around. You're either getting away from your opponent or closing in on your opponent. When you are in range of your opponent, you can only throw one punch. That's it. No combos allowed. The closest thing you can get to a combo is when you're in "Rumble" mode and you fire off a punch a second.
The difficulty of the game isn't hard until you fight the last opponent. Then it jumps from quite easy to insanely difficult. The training in R2R is alright, but it can be improved upon. There are also not as many characters in the game as the PS2/N64 versions (Only 11 playable characters in the game).
Overall, this game is pretty disappointing. It looks and sounds good, but it doesn't having a feel of boxing to it. But at least you get to play as Shaq or Michael Jackson. This game's got that going for it.