Need to improve
The idea is fine, but as zindelo said, with your upgradesi'ts almost imposible, i don't know but at leat i didn't find an option to regenerate my sphere health, so i lived just with my shield, and as sebine said, you feel like you are being told what to upgrade and stuff.
so most of it i'ts the upgrades, low gold, bad upgrades, very difficult, it would be better than your sphere regain full health at the end of the level in that case, good idea, bad game, improve it and call back ;)