Good idea!
I understand your idea that gravity controls your ship, and it adds a pretty nice challenge to the game, but there's not enough depth to the game to make it work. I think that if you're supposed to release the mouse to shoot a beam, it should at least charge your shot to make it more powerful ;) You should add upgrades and then maybe the whole "gravity" concept would be a lot more substantial rather than being a nuisance. I hope to see this improved in the future! Nice start, though!