The art is really great and the music goes along with it well.
I think you aren't doing a service to the art with the lighting (Or maybe it's post-processing), it seems to wash out the art a bit (I remember seeing you post in the discord with the art assets and they looked quite different). Perhaps the contrast is too high?
The tutorial was quick enough, glad I got to place units fairly quick. The "Run Sim" idea is a bit weird for what is basically a tower defense, but I understood after that that it's really more of a tower defense simulator.
It felt bad that the heroes were attacking my units even though they were so far from them. It would be nice if that was communicated better (I figured if I placed them with enough range from the hero's path they wouldn't be reachable).
The traps were super cool, I loved that I could place the spear wall on top of the existing walls. I was a bit confused when the flame traps seemed to only be one-use, would be nice for things to be less disposable. At a certain point (the wizard and rogue were half-way thru), I was feeling like I should be either getting more mana or being able to upgrade my units. I had four units unlocked at that point and it didn't feel like it mattered much which one I placed down.
Overall: Awesome idea and execution! I think a "turn-based dungeon defense" is a cool idea that I would maybe play. There just needs to be some more thought put into the units. Personally I wouldn't play more because the units had no real "growth" or permanency to them, they all just felt disposable which wasn't as interesting.