I really enjoyed the concept! If you could "rescue" blacked out pieces at after a cooldown it would've been even closer to the Gain Ground.
Did you experiment with having the canon ball shoot out of the cannon body? I think it would've made it more unique and make having two canon bodies a bigger bonus. (these controls would probably make it harder though, so understandable to keep it simple.)
It's really sad that it doesn't have any audio, otherwise it was great!