Story mode is tedious, and bugs make any difficulty above "easy" near-unplayable. Re-balance the game's focus, and fix bugs (such as one particularly irritating instance where one time out of ten a blinding ninja won't die when you type the required word).
Blargh. This game has a lot of problems. One, the enemies don't die on the spikes. Two, dying should reset your ammo count to whatever it was when you entered the stage.
Far too easy, and obviously programmed by someone with zero idea of how playing the guitar actually works. 3/5 because of the pretty interface and bug-free gameplay, however lousy and unintuitive.