Very well made game! Here is my honest review:
Pros
- Mechanics that remind me angry birds star wars :)
- Nice space background music and SFX
- Very nice interaction of gravitation and collision physics
- Fun boss on last level
Cons
- If you give medium shoot force it still flies too fast. So it's a bit difficult to pick right strength to shoot
My suggestions/improvements
- Add text for level 2 and level 4 that hints what you need to do. I know that you can read it in description, but if you would continue working on this game, it would be really cool
- Possible new mechanic: you can add buttons. Your main goal is to hit all of those buttons (1 or more buttons) in order to open a gate (or move away something from your way) that will allow you to get to the planet.
In overall I really liked your game. I hope you will continue to manage it further and release a full game. If you didn't understand something from what I have said, feel free to ask me.