You could change the enemies into something familiar like zombies or some other cliche monster, but if you want to keep your original enemy character then maybe try drawing it from the top view since it is a top down shooter. Instead of making just the gun follow the cursor, maybe make the whole player's body + the gun follow the cursor. You should try change the cursor into the cursors seen in most fps games and maybe you should change the backgrounds into grass plane, stone floor or into an urban setting or something. Also it would be beneficial to the game to have a 2 second delay before you spawn the enemies when you start the game.