Monsters, inc. is one of the best animation film ever produced, only surpassed by The Incredibles.
The animation itself is incredible, especially if you take into consideration the work that was done on the hairs of Sulley. The world they created is without par, extremely imaginative and full of details, and that's without mentioning the mechanics it uses to get energy, as well as the energy crisis within.
Each monster is well thought, wild in design, and nicely rendered. The colors are great, vivid, and cheerful. The humor is plenty, side splitting, and almost non-stop. The jokes are great, and the dialogs complete, natural, and logical.
The only negative thing I could say is that the "evil" part of the scenario was a little unimaginative, but fortunately, it's not the main attraction. The main draw is the relationship between the two main characters and the little girl. It's adorable. That alone makes us fall in love with the movie.
A must see.