Interesting game, i was a bit lost at the start becasuse i knew how to place stuff but not if i had to protect only what I've placed or something else and more importantly, where the enemies would come from. Once the round started it was all clear though, but i think a introduction could help since you can't modify it while in a wave.
The controls are easy to understand and you can also click to pick what to place which is nice, but you've forgotten to mention to press R to rotate objects.
Also, somehow even though i had my castle fully closed, a enemy made it through the walls without destroying them and i died from that.
Cheers, i hope this helps ;)