Alright, I'll give my honest opinion, first, the good points:
The music is really great, along with the title screen.
And it's really creative that you made a working Game Boy like screen border which actually shows the buttons pressed.
But for the Cons:
Even with the instructions, it's kind of hard to know what the game objective is, this could be improved by adding a small synopsis like: "Plant more corn seeds and defend your crops with wood walls" or something along those lines.
There is just 1 more control that are more than what a Game Boy can have, and the rules state only max 8, maybe you could take away one control with a mechanic that doesn't impact the game a lot.
And lastly, there seems to be more than 4 colors on the screen at once, even if the Game Boy border is not counted. And there is the bug where the square to indicate block placement is off centered or something.
I can tell that you are an experienced dev since u already have a lot of games published (and a nice itch.io page), and that I understand that this is just a Jam game and bugs are expected, but if u are planning to update the game to make changes, that would be really swell as this does seem like a good game idea. Other than that, great job and I hope u had fun in the Jam!