I played this game on stream: https://www.twitch.tv/videos/1850361813?t=02h22m05s
My first game was really weird, I didn't know what to do, so I just watched the enemies come and destroy me. I was trying to click on stuff, but nothing happened.
After that, I realized I needed to purchase stuff, build them, then start the round. I think a tutorial would be super useful here to teach players how to play the game.
Another suggestion would be to add some gameplay during the rounds. It felt like once a round started, there was really nothing for me to do except watch, and either win and buy more upgrades, or die. Maybe having some abilities like AOE for the player, or getting a tower to fire faster, or something, would be good.
In terms of the UI, there were some hexagonal pieces and square towers. I think the square towers also fill up their hexagon in terms of blocking movement, so maybe instead of having different shapes, use different background colors?
Also, having sound and music should really add to the game ambience and enjoyment.
Overall, I think the concept is interesting, I liked the setting of game dev stuff. There's a lot to improve here, but it's a good kernel!