This prototype is amazing!!! Though theres lots to improve, here are my suggestions:
-You should be able to select multiple(maybe up to ten) humans with a box style of select(like on windows desktop)
-The text should have the highest order in layer, because when i put down a bunch of spikes next to the altar, I couldnt see how many humans I still need to sacrifice
-When I first bought a human, I thought it places it in the world somewhere, so I purchased multiple of them, then realized that they have spawned behind the button(though it makes sense with the farms and spikes) This could be fixed so you cant put down humans in that ui section
-I know this is a big feature, but I would still like to see this in game: a turret that can shoot the monsters. It could have a small area of sight, and you could make it so that it costs multiple resources eg. 30 wood and 50 crystal
-I also think that there should be a way to automize stuff
Please continue working on this project!