Time Out says
Pixar's computer-animated rumpus comes to you from Monstropolis, a pastel-coloured parallel world populated by largely peaceable beasts. Sure, some do victimise small children, but purely in a professional capacity: they're the scarers employed by Monsters Inc, the city's scream-fuelled power-generating corporation, to prospect kids' bedrooms and harvest their most piercing shrieks.
Take James P Sullivan (voice: Goodman), a horned, shaggy-haired colossus, and the company's star scarer: off-duty you couldn't find a more genial creature, except perhaps for his assistant Mike Wazowski (Crystal), a green walking eyeball who's a hit with all the chicks. Life's smooth scaring, until the unthinkable happens: a small girl called Boo crosses the threshold into Monstropolis. It's common knowledge those things are toxic. A raucous underworld escapade, this is as vibrant and colourful as Orphean comedies come.
It's unfailingly lively entertainment that doesn't stint on (earned) feeling. Ideas about fear of the unknown, industrial corruption, and the splendours of polymorphity are all taken in stride. The balance tilts towards action and gags, and does them gloriously.