Very nice graphics, decent sound. I think the concept of influencing the gravity of objects with your alien ray gun is brilliant, and lends itself to some good puzzles.
That said, I had some difficulties with the game. I think the platforming is just a little too finicky. I had a hard time making a number of jumps. You should consider implementing coyote time.
Also, I was not always able to shoot. It's hard to describe this issue with precision because I couldn't figure out how to reproduce it, but sometimes I thought I was out of ammo, but I wasn't--the gun just wasn't firing. I'm not sure what was behind that.