I absolutely love this concept, I have a tiny bit of experience with drag and drop programing like this, but there really needs to be some instructions in-game. I repeatedly had to tab out and there I found most of the button indicators were blank spaces... It took me a while to figure out shift-clicking was delete, P was the play/pause and I still don't know how to switch spells. I'd consider an in-game tutorial and walkthrough of the different parts to be the biggest priority for the sake of accessibility, as well as turning on your comments section here for feedback, it's going to be paramount in a game like this. 

PS. Instant kill death fans in a permadeath game aren't fun when you're learning... :(