The multiculturalism is almost Caldecott-bait. It's like it was specifically written to appeal to givers of children's book awards. It's not a bad message, actually, probably not a message at all.
It's pretty stereotypical. Very American, with the Fourth of July, baseball, Halloween, Thanksgiving, and the obsession with Christmas in December. There's not really much to it, with no storyline or message.
Mundane walk through the forest with fanciful animals.
There's no real message. It doesn't really go anywhere. The animals don't really do anything. There aren't any characters. Nobody really has a personality.
It presupposes a world where mice are intelligent and humans exist but don't realize that the mice are intelligent, which is kind of a difficult world to live in when you realize that we kill mice for pretty trifling things. But, you know.