Core Mechanic -> The infinite upgrades is a really cool feature, it allows me to have ridiculously powerful towers, which is what makes a tower defense fun!
Game Feel -> Very satisfying. Ignoring the upgrade bug I really enjoyed playing.
Visuals -> Very nice! The grass and road textures work pretty well. My only issue was I didn't really have a clear understanding of what all the towers and such did.
Audio -> Love the music and the changes, and the SFX chaos at higher levels!
Theme -> I'm not entirely sure, though I suppose you start small and then it gets big.