Not the most original idea, but it was a solid game. Pacing was nearly perfect, I didn't feel overwhelmed in earlier waves but I was never underwhelmed either. It was fun to play. The purchasable upgrades made the game feel complete, and the player controlled placing of the turrets was a nice touch. The farm music made me smile, but it wasn't loud enough. In fact, all of the sound could use a boost. This was by far the smoothest Unity game I've played in a browser. How did you do it?
The art was good for the style! More details could be added of course. Would love to see more particle effects and shading.
Overall, the game was a strong entry. I really enjoyed playing it.