This game quite good overall. I enjoyed playing it. It has just the right level of difficulty/challenge. It's simple and engaging, this is a very good combination in my opinion.
I think it could use a bit more sound effects and probably some sort of background/ambient music.

Although it uses ads I'll play it again.

Very insightful comments, I'll be sure to address all of them.
Thank you very much!

This is a cool game. It looks original. The planet effect is very nice.
I agree with the previous reviewer that the game is a bit challenging.
Overall I think the idea is nice and this initial implementation is a very good start.
The one thing that felt a bit odd is that there's a small delay after you fire and before you hear the sound effect.

Yes, a Mac build will be available with the next version of the game.
Cheers!