Cool concept!
At first I didn't get that you could stack blocks to build the towers and try to fill the field...But then it got easier :) I didn't pay really much attention to the type of blocks and just tried to create the highest possible towers. In the end, when it got pretty intense, I just placed the blocks everywhere to slow down the enemies, though I am not sure it worked, but I still managed to win :D
I would probably prefer to have shorter rounds but faster pace — I think it is pretty chill in the beginning for a long time. But it was fun!