Spritestack art was super neat and I loved that you were able to pan and rotate the map around (the tile that's highlighted being spritestacked was also super neat), genuinely felt like a 3d game. The one thing that broke this immersion for me was the goblins. They were super low quality compared to the rest of the art in the game and I think going back and improving on them (whether better sprite quality or spritestacking them as well) would be great.
The gameplay is pretty basic, but fun for a while like all tower defense games. Different tower upgrades besides just stat increases would be cool, but I understand keeping the scope low for a jam. For a jam game, the gameplay is super well polished and thorough!
As for theme, it's generic, but it works 👍
Great game!