Took me a while to realize I had to manually plant the crops, and the menus were a bit too blended in which made them hard to locate initially within the short time frame in-between the waves. A 'Ready?' button for starting the next wave would've been pretty nice.
Other than that, once I started to understand the game though, I began enjoying it. It's a bit difficult to hit the targets though since you don't normally expect the bullets to just pass through the rocks but I eventually got the hang of placing and timing the explosions reasonably well.
All in all, really fun game and a nice idea.