Confusing!

This drama was honestly so confusing?? It started pretty well and I was so excited about it cause the idea of this giant hole on the ground which creates those monster was thrilling but then, at some point, too many things were added to the story to the point where I stopped trying to understand what the hell was going on and I was just trying to catch up with everything. Nevertheless I appreciated this cast and their acting, if the acting wasn't this good I would have dropped this drama at episode 3?