Wow this is crazy how did you come up with this from the theme.
The core mechanic is actually really fun I like it. You walk around doing quest, it's kind of like the cooking game like overcook where you get stuff to do stuff in time limit, but opposite. It is quite funny when you kill the enemy.
Although after playing for a while there isn't anything new so it get quite repetitive but I think you definitely scale the game up with more features, harder wave and upgrades. (I think this game with co op would be spicceey)
The art is very nice I really like the pixel art and you definitely can identify which farmer is which and what to kill first. The art remind me of starbound. I have one problem with the walking animation which is a bit weird, it look like your dancing or something when you run. (it look good on normal walk though)
The sound effects is amazing, it really make the game more satisfying. Although it would be nice to have some music with this kind of game.
I think how your character physics interact with the alien is a bit buggy.
Overall very solid game with potentials.