Thanks so much for the great feedback! I'm glad to hear you enjoyed the game.
I have gotten a taste of losing upgraded towers during play testing, and it really surprised me how much it stings even with 0 investment into playing! I look forward to adding more difficulty and a lot more content in the coming updates, and I have some ideas to make sure it doesn't feel unfair.
The UI is also something I want to rework a bit in the next update. I have been taking heavy inspiration from Bloons TD UI but if you have any ideas for making the placing of units more intuitive it is highly welcome. I do plan do add some hover effects to placed units to make it more obvious you can click on them
I have also added more in depth tower targeting already which fixes that issue and gives you more control, coming very soon!
PS: Id love to try out your game but currently the only computer I have access to is a Mac. If you are able to release a web or mac version I can give it a try!