Truly amazing visually, love the effects and the use of the art assets. Laser burning things and the spread of the shotgun shots were especially cool-looking. Controls were also smooth, and handling the UFO had a cool momentum effect that felt appropriate for a flying saucer.
Gameplay-wise I found myself having to keep luring the farmers away, go make a quick sweep at the cows and repeat, which can get a bit monotonous in the later waves. Killing farmers had little use because they respawned so quickly. Maybe you could make the cows and farmers spread more on the terrain to encourage a more dynamic type of play?