Ill just put my concerns/suggestions in a list:
-dragging humans give me carpal tunnel/hotkey to sacrifice?
-human freak chamber too op/ voids the consequence of sacrificing.
So right now the first level(tutorial) feels like a proper level 1 while the second one was just level 1 on hard mode.
Suggestion: expand on it, add new monsters for new levels, new structures to deal with them. I REALLY like the idea of sacrificing. so maybe human sacrifice would get u a certain resource that lets you buy a certain structure to easily deal with a boss that comes out fixed minutes after round starts.(lets players decide to more easily deal with boss, or take the risk and complete faster.)