When I first saw the 'physics' part, I questioned what was the point of it in a tower defence game. Then I actually played it and watched the bugs move.
It's weirdly satisfying, like watching water flow and I love the fact they move at 'random' preventing easy prediction.
I think the power on each level quite a restrictive way of preventing cheese, at least for me, I ended up with too much money, not enough medals and everything I could level up, being levelled up. I think having an 'unlimited' power option, or it being a mode for once you beat the levels would be great.
As well as that, I think an option to refund upgrades without just yeeting everything off the table would be great, as constantly having to rebuy the same upgrades and memorise where I put X and Y stopped me from experimenting which I think is a really fun part of the game.
People already mentioned the main gun losing usefulness, but I wanna shoutout the cannons.
The slight knock back, at least for me, actually prevented the bugs from attacking a barrier making them perfect for creating killzones.
Flamethrowers are amazing and I just like watching the missiles. The shotguns are neat, but as someone else mentioned, the lack of killing power made me only use them if I only had enough power for them.
Didn't really experiment with the sniper rifles, I at least, didn't really notice much difference in killing power despite them being full level.
Again, I feel like that limited power really held back experimentation but other than that, I had alot of fun.
The graphics, the sound, the design.
Good job on the amazing game!