Part of the problem is that Pixar has set its own bar so high that it's hard to keep going over it. This movie was not as good as the first one, nor any of the other Pixar classics. I can't remember a single great dialog line, it was slow to start, and the plot is formulaic and cliche' out the wazoo.
Also, the animation has gotten really good, to the point where it's uncanny valley all over the place. This was particularly evident in the pre-movie short, which was an utterly grating sexist bit about a male and female umbrella. Dear Pixar, just in case it wasn't clear GIRLS ARE NOT ALWAYS RED AND BOYS ARE NOT ALWAYS BLUE. Also, plots about males making heroic efforts to chase females are ARGH-tastic in and of themselves and trying to be endearing about inanimate objects is very good if you're Disney and it's the 1960s but come on, you can do better than this.
Thinking about how annoyed I was by the pre-movie short caused me to realize something about the feature. First, Monsters University doesn't have a villain(ess) per se. It's the story of two guys struggling for acceptance; it's a story of nerds and jocks, cool kids and uncool kids, etc. But there's not really a bad guy in there.
Instead there's "Dean Hardscrabble" who is voiced by the incomparable Helen Mirren. Hardscrabble is scary - she's a monster and supposed to be scary. She's harsh and demanding and she sets obstacles for our heroes. She has all the ingredients that you would expect to turn her into a typical Disneyesque villain - the vast majority of whom are women. Whether an evil stepmother or a wicked queen, you know the type.
But somehow that doesn't happen here. Hardscrabble is a demanding individual, but she isn't evil. She isn't even mean. Her character has more to it than any other female foil I can recall from a Disney film. She reminds me in spirit of Elinor, the queen in Brave, though Elinor is a support, not a foil.
And that led me to another sense of how this film differs from your typical children's/Disney and even much adult movie fare: actions have consequences. The fact that someone is a named good guy doesn't mean they automatically can get away with breaking the rules. Poor choices lead to poor outcomes. Yes, there's a lot of overdramatization of certain bits but the last 1/5th of the movie does a remarkably good job of handling outcomes.
Now if only the first 4/5ths had lived up to that standard.