Simple idea but that's really not a bad thing. Good job on finishing a game. I had fun playing it :>. Maybe you could change a few simple things to spice it up. Make the movement more responsive it (almost) always feel better to fight the enemy and not the controls. Also you could change the score system so that it is not timer based but on pickups for example. That way you encourage the player to move through the map and not to wait in a corner and watch the score go up.