The game has no sound at all, which is a huge minus as video games are an audio visual experience. And sound design can enhance the experience in every way. Enemy sounds, music and more.
I liked the upgrade system and controls worked well. I got a final score of 325. The game was way too easy though. I think one enemy who can shoot something back would have given the speed upgrade a real purpose. If there were obstacles like walls or spikes or something it would also be more challenging as you need to plan your movements. You could change the layout of the traps every wave, so the player need to learn new routes every wave.
Right now you just run around the enemy's in circles and keep on shooting. It was a little dull in the end. But it is a nice idea to work upon.
I didn't get the theme though as the game was too easy, there was never a reason to choose regular wave.
Even if it's only 5 minutes, I would recommend adding a pause screen as sometimes you might get to the door or answer a call and then you cannot pause the game.