I liked the game idea, the martians are never up to any good...
The energy bar goes down maybe a bit too much at once i think, and in reverse I think the planet loses too little health :D. Also the UI should be anchored to the lower left corner, now it kinda floats in the middle of the screen when the scene changes.
But those are just minor nit picks ;P
Honestly good job for making a game in this short amount of time:!