Hey, Nice little game you got there. I'm going to explain my vote and what I think you guys could make to make it better.
Theme: 5. The game goes nice with the themes. ( You guys used the 3 themes as well).
Fun: 4. I give a four because I really liked the gameplay loop and I'm really into these type of arcade games, but I could be better of course. One of the main things is that there's no use for the crops except from the score, you could just run around killing the aliens if you don't care about that. I think maybe the crops could be the ones to give the bullets or regen the life (just a suggestion). What I realized is that after a few plays I did'nt few soo compeled to play it again, but the first times was just fine.
Controls: 4. They serve the purpose, I like the hook and the shotgun, but overall nothing super fancy.
Graphics: 3. They serve the purpose, but they could soo be much better. One of the main things is actually understanding the most important things and giving it contrast. The farm floor was the same bright as the character and the crops, you guys should try to push the visuals of what matters to the player; make the aliens bigger and the background not as distracting.
Audio: 3. Good. but I'm not that good on audio stuff to give proper feedback on this.
Originality: 4. A good game, that fits the theme propperly, you made a good job with what you got, and is actually original in it's simplicity.
Overall is a good game, I think with a little more work on could be a fun replayable game.