Ok, so this was pure fun! I'm not a fan of tower defense games, but this one got me. I was able to complete it and I felt like I needed more things to defend, haha. I can see how this game can be expanded, like different ships, power-ups, and obviously levels. One thing I would want to change is the speed at which the ship moves, maybe it would be better if you could move by just pressing the key instead of smashing the button.
Very solid entry.