Fun game, I nearly played to completion but didn't end up finishing the last stage. I think the biggest problem I found was that there was too much going on from the very start of the game. This problem is two-fold:
1) As a player just starting, having 12 attack options in addition to 3 movement options is WAY too much for the first level of a game with no tutorial. It was really overwhelming and I was reading for the first minute or two of my playthrough.
2) Because you have every attack option available to you upfront, this means the player doesn't get any more powerful throughout the game. This poses a major issue because the enemy waves increased in power dramatically (Maul slime and 1-shot Blue slime I'm looking at you). This makes the game feel way too easy in the first few waves and way too hard later on. It also makes the game feel stale because there isn't anything to play for or unlock as the game goes on.
The best tower defense games are really successful because the player starts out with a very vanilla tower/unit and can either upgrade or buy more powerful towers/units as the game progresses to match the power creep of incoming waves. I think if you switched to this kind of model, the game would be even better than it already is!
Sorry for the essay, I think you guys did a great job and I really appreciated some of the smaller details like the animations of the map building/disassembling and the random quotes :)