It's a great idea and it was pretty well executed, the problem I experienced is that the letters that show over the action icons to tell you what key does what were incorrect. It could use some more consistent graphics, the ui is pixel art while the in game graphics are just circles, it would even improve it if the circles were pixilated. It could definitely be made into a full game with some polish to the graphics, toning down the difficulty or at least create difficulty settings, and maybe add abilities and upgrades you can buy in a type of store in between waves.