1. Controls - Unlike SMB, these controls are pickup and play, and they aren't that innovative, but they handle extremely well. You just lean your iPhone from side to side to control the arrow. That's how simple the controls are.
2. Replay Value - The replay value on Cube Runner is one of the highest in the entire App Store. It keeps track of your high score for that level and it's fun to try and beat you record, over and over and over and over again.
The only other stuff worth mentioning is that the graphics could be polished a bit. Overall, this game is simple, addicting, fun. It is worth the download from the App Store and, it's free. You can't beat that.
UPDATE: Cube Runner is no longer available for download in the App Store. This is because of some errors that occurred whilst playing the game. The developer has stated that he will update Cube Runner and it will return to the App Store once it is revised.