It has attractive clear illustrations of one animal per page, a simple repeating structure with only a few new words each page, nice rhyme/meter. Its structure involves repeatedly anticipating the next animal, which makes it easy to memorize.
It is a book my kids enjoyed “reading” aloud to themselves at age 1.5–2 before they could fully remember the content of more complicated picture books.
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Of course, this isn’t the only type of book small kids should be listening to, and in the genre of extremely simple picture books there is a lot of abject garbage.
But I'm not actually opposed to the basic structure of "animal color" that Brown Bear has, I think it could retain that and somehow also get more effective nuance. It's entirely superficial. Note also that 2yo's don't have an experience and relation to classes and teachers, so that doesn't even fit. The very same structure could be less arbitrary and be used instead to connect associations that are worthwhile making for the 2yo's, the way that Hungry Hungry Caterpillar doesn't just show randomness, it actually fits a real biological context.
Adapt Brown Bear to highlight an ecosystem that goes together and it would be superior and still achieve all the same interest in the 2yo's.
Another one in a similar vein, which my kid liked, was "Here Are My Hands"
Brown Bear, Brown Bear from Carle himself is mediocre junk. It's just colors and animals, and has no character, no narrative, no arc.
The Hungry, Hungry Caterpillar is an amazing, astounding masterpiece. It is usually printed with a sort of dynamic tactical approach with different page sizes, holes in the pages, the story has a real arc, it teaches biology, it carefully works in numbers and days of the week and the idea of time frame… it's a true stand-out.
Most of Carle's stuff is somewhere in the middle, though he has a few other superb ones.
Just like art for older audiences, there really is a range. You could say that all movies are the same: people having conflicts and doing stuff. On some level, they're all dramatic and simplistic.
It's not mere taste. What makes a great book or movie for any age is not total relativism.