The gameplay is very good! The shooting and controlling the character happens smoothly without hiccups. The aesthetics are very clear which is important for such a fast-paced game. The music and sound effects fit the game, too.
I like how the black holes were a double-edged sword - you could use them as cover and trick enemies to walk into them, but might accidentally walk into them yourself.
The enemies seemed to have too much health, though. Also, it might be useful to have different colors for enemy bullets than my own to make sure the player sees them coming. Oh, and I don't think there was anyway to see your high score.