I think it was okay, but it has a lot of potential for you to make this more fun. I think making the boxes not just go faster and spawn on the sides after each other, but keeping the speed constant but increasing the amount of boxes could almost make this a rhythm game. A highscore would also be nice.
Viewing post in Box defending itself from boxes using a box jam comments
Nice idea!
I did intend to make the game over screen display a score based on something like the number of boxes you destroyed, but decided against it when I saw that there was 10 minutes left (before the added time). I didn't think of a high score system, though. I also didn't think of the more boxes over time thing.