It's not that Monsters University is a bad movie. It's just... unimaginative and feels rather tired.
There are also the sentimental life lessons that so many "comedies", particularly other Billy Crystal films (one thinks immediately of City Slickers or Throw Momma from the Train or Mr. Saturday Night), feel that they need to teach us instead of spending more time telling jokes and making us laugh. In Monsters University these pearls of wisdom include:
1) The cool people are not really that great to hang out with and are actually a little mean. Instead of trying to spend time with the cool people, look at the group of nerds with whom you are stuck: some of those guys are pretty interesting, even if they are totally socially awkward.
2) Being a total control freak and a nerd really pays off in the end.
3) Sometimes you actually can't be what you've dreamed your whole life you wanted to be. A little cyclopean monster who resembles an olive with legs is not scary, no matter how hard he wants to be.
4) And last but not least: friendship, man. That's where it's at.
Now I'm not saying all these sentiments aren't lovely, I just wish I spent more time in the movie laughing and less time "learning" lessons like these. I put learning in quotation marks, because no one here is actually doing any learning. When a movie spends most of its running time confirming my beliefs about children, friendship, morality, teamwork, etc., and telling me things I think I already know, I generally start to feel that there is a problem. There are lots of new things to be said about friendship. And there are lots of new things to be said about popularity, homosociality, teamwork, nerdhood, and social awkwardness. But Monsters University sticks with the old clichés.