I like the idea
This is an original concept, and could be fun for a long time. It makes me wish I had an optical mouse. I quite like how the black balls can be directed into the central ball in order to push it closer to the middle if you are skilled enough, and the upgrades and the boss defenses make it a bit more addicting. The only down side (other than that I suck so much at it) is that it might be a bit too simplistic. Perhaps different arenas with various obstacles and a greater selection of enemies and upgrades would help with this. Over all though, a good job.