At first wasn't clear what to do. Tried to shoot myself and couldn't move (tried WASD). But after that it was quiet easy to grasp.
Loved how the "radar" was around my character ... but I didn't know where to place the towers, so placed them all over the moon ... but then the asteroids came only from 1 direction. So was a bit confused if I should've kept most of my mana from the start.
Overall great submission.