The best part of the game was when this alien with screaming mouth showed up:D Would be silly if he would start eating the other aliens, and that way he would be another way for the player to advance.
Also, the bouncing bombs with the player ship was really cool, wish this would come often. Maybe it would be nice to see the what will be the next bomb, like in tetris?
Anyway, I would make the ship accelerate more, and allow it to move diagonally - this would make the feel better