Pretty cool, simple game. I could really see this being a successful mobile game! The graphics are not amazing, but still passable. Although it's interesting that it looks like the game is built in 3d, even though it's a 2d game. Interesting choice.
A quick suggestion. When you build up "charge", it shows a numeric value next to it. Why don't you get points for switching with more charge? Seems like a missed opportunity. Maybe that would make the game too complex, but I think it could be interesting. Of course the game is fine (and addicting!) as it is. Good job!
Also, maybe you could check out and rate my game? :)