Been a while since this post, but yours is such a good breakdown that I felt like responding. I actually avoided looking at comments for this long because I knew what a flawed experience it was. I'm at peace with it now.
Very much of the game's problems came down to time; the scope was too large for a single programmer, (myself). I actually had a lot of systems that I didn't have time to properly implement. The map is procedurally generated, but I didn't have enough time to make as many room layouts as I would've liked, so it ends up having the unintended side effect of making all the rooms look the same, which makes things super labyrinthine and frustrating. I wanted to create a navigation system, whether it was a map or an arrow telling you where to go, but I ran out of time. I also had ideas for more enemies, and more powerups, but nearing the end of the week I crammed the boss fight into the last day to give the game a proper ending, and then posted it, very stressed. As a result, the only enemy I had was the UFO, and that was implemented the second to last day. Didn't have much time to test spawn rates.
Put simply, I appreciate and agree with all of your criticisms. I had plans for most of the issues you brought up, but had not enough time to make them happen.