I like the concept of being able to change direction of fireballs mid air! I don't think it needs to be a mouse click though, make it a keyboard button. And I would keep two separate buttons -- one for placing fireballs, one for using them. play around a bit with making the fireballs move in 2d space, maybe using the mouse. I could see some fine sniping-behind-corners mechanics with the fireball.
I think the difficulty is really high as well. I would add a health system, 1 hit kills are punishing.
Side note on music -- if you plan to make the music for the game, I recommend a few reading resources: The complete idiot guide's to music theory, and the complete idiots guide to music composition. If you understand a bit about scales, chord structure, you can use any DAW to make solid music by sticking to basic chords and basic movements on the major scale. I knew very little about music, those books taught me a lot to make passable music.