+ Interesting idea that addresses the prompt
+Idea presented in a way that is pretty clear and easy to understand
+ Everything appears to function as intended
+ The upgrade shop was above and beyond, for the time you had.
- It can be hard to respond to the directional changes. It goes beyond being hard to predict and delves into being hard to react to in a meaningful way. If you develop this further, I'd reccomend experimenting with bigger direction changes done less frequently.
- The waves are LONG, and there can be a lot of dead time. I very nearly didn't see everything this game had to offer because of it.
You've got a pretty solid game here. Most of my issues with it are a matter of tweaks and balances. Develop it a bit more, inject some character into it, and I'd legit play it.