Couldn't have asked for better feedback. As posted on Reddit, I am replying here too, for the benefit of other players who might want to contribute here:
Wow, your feedback is amazing. You got the gist of the tension I was trying to build. Everything you said about things that can be improved (hold and click vs. just order build, OST being too much at the start, big enemies, and the lack of a tutorial) makes sense to me. I was half aware of the lack of a tutorial but was probably overconfident that players would get it.
Haha, those things at the top and bottom are some of the most interesting things - they reflect and boost your bullets and get more exciting the more you do it. I totally get why players might miss it altogether.
Thanks for such detailed feedback; I love it! I will definitely work on those and update the game.