Yeah, I don't know why, but I felt like I was 'cheating' when I used the keyboard. Besides, I guess having to sing the songs does add a bit to the atmosphere although there have been times when I've been in the midst of a battle, frantically waving my mouse around trying to change form when something (usually a nautilus, hate those) hits me in the back and kills me, but no worries.

And I've been spamming with the mouse through most of the game and no cramps yet! (although i'm using a laptop)