Pretty good!
It needs some omprovement though.The enemies should be able to hurt you,you should be able to die.They shouldnt appear at the same places all of the time.Also add:
-More levels
-More weapons
-Background music
-Stuff in the background that you can shoot as well
-Different difficulty settings
-Different characters to choose from
Then this will turn into a kickass game!Keep up the good work!
-cd-