This game was really fun! I wouldn’t have been surprised if I saw this listed in honorable mentions :) I really enjoyed getting so powerful that the enemies were blasted off the screen as soon as they arrived. There were so many projectiles flying around it sounded like popcorn popping!
Now onto what can be improved:
Gameplay: Carrots are overpowered. You literally don’t need any other type of plant. Ideally each plant would have their own special use case or be part of a strategy the player could use. It would be pretty cool if you could combine plants to create special plants, that would make for interesting gameplay.
Content length: Only one level, but I had fun replaying the level multiple times. Still, if your goal is to get in the top 3 of the game jam, I think you would need multiple levels.
Sound design: Satisfying, but doesn’t sound polished. I would try to find different sound effects. One tip I heard (and you might have already done this because the effect is subtle) is to vary the pitch. See https://www.reddit.com/r/Unity3D/comments/18ycc02. Note because sound is already satisfying I would put this low on the priority list of what to improve.
Theme: Theme is excellent. Saving the environment is a classic, and that theme is told well through the environment design and gameplay. No improvements here :)
Environment design: Good. No suggestions.
Character design: In this case the characters would be the enemies and the plants. Excellent job here, the animations brought them to life. Plenty of variety when it came to the enemies. Could be more variety when it came to the plants.
In summary, I think the main things that could be improved are the gameplay and the content length. Let me know if you update the game, I’d be interested in playing some more :D