What an awesome concept, and fantastic execution to match! I really loved all the layered mechanics, which worked excellently together to create a tight gameplay loop. The particle system gives the game more visual oomph and a lot of polish, too!
I really enjoy how you employed all of the interesting mechanics and incorporated them into upgrades, which gives the player more to look forwards to in contrast to simpler games in this genre with predictable damage/movespeed etc. upgrades. The love given to the design board shines through :)