Way to easy. Instead of a gun, a ballistic weapon like a bow would be cool or at least a way to shoot in different directions, so enemys could have areas where they could be hit and some where they couldn't be hit.
That is a very great idea. I had looked into that, but this is only the second game I have made and the time wouldn't allow it. If this game is liked enough, I have plans for an actual game with a similar style, but more mechanics and it would have more to do.