This is a great concept. I really like the capture and throw mechanic.
The texture tiles on the floor were very confusing. It took me several times playing before I realized that they weren't obstacles. It would be nice to have them be a different color, something to distinguish them from the walls.
I think, but I'm not completely sure, that I would have preferred a more arcade style movement for the ship rather than the more realistic style. At very least I'd like the ship to be a bit more agile. It felt very cumbersome and I don't think that added to the game.
It seemed odd to me that the rocks impacted the walls if they were floating around but could pass through the walls when I had them in the tractor beam. It would be nice to remove that inconsistency though it might require making the levels a bit less cramped. Similarly, I was expecting that the rocks in the tractor beam would block bullets and was surprised when they didn't.