I really like the idea here. Tower defense but with one big scalable tower. This is awesome dude. The simplicity makes this pretty fun and it's one of those games where I think you found the magic pretty quickly in the prototype/jam game! Now, if you wanted, you could easily scale this to add all sorts of fun content.
Personal Preferences: Some flashier art and music/sfx. I understand it's a jam game so not knocking your rating because of this, just saying, I could see this game become super popular with a little love for the presentation.
Overall though, I enjoyed playing this a lot and could see how it could become an incredible game. Great job and congrats on your first game in 25+ years! That's awesome!