Super fun and addicting to play! The player has meaningful choices to make throughout which is great.
The concept is nice and easy to pick up with some subtle strategy in there too.
My main critique is that the enemy health leaps too much in the starting rounds. I found a lot of the time if I didn't have the right mixture of turrets in the first 2 waves, I would just restart the game because I knew I wouldn't make it past wave 5.
I think the difficulty spike for the game should be a bit later, like maybe wave 10? Because then if the configuration of towers is too weak to survive it'd fall entirely on bad player strategy, rather than a bad run of RNG.
A wild suggestion I would have is to maybe have something the player can do during the waves playing out beyond modifying buildings? When you don't have money or any buildings you want to sell/merge you're sort of waiting for the wave to end, which isn't a grievously bad thing, it's at most like a minute of waiting. But I think maybe some sort of passive boost you can grant to a single building, or maybe clicking on certain enemies to slow them down temporarily (with a cooldown of course) could give the player something active to do while the wave is playing out? Would really depend on how it tests, and of course you don't want to overcomplicate the game, just a thought.
All in all really solid job, I thoroughly enjoy playing it and will definitely revisit it from time to time.
EDIT: Still haven't beaten the game but it's definitely much easier to make some progress! The change in tower behavior is much appreciated and really helps with the higher health enemies. PS: If I were you I'd just block that rphb guy, he's whiny and angry with literally every game review he does regardless of quality lol