Another great movie from Pixar. Certainly did not disappoint, and I echo what the others said: It is markedly darker than its predecessors, and some scenes might be scary for very young children.
I must say that this movie is a real emotional roller coaster, and I shed man-tears in the last quarter of the show.
Basically, for those who are on the fence, stop waiting for reviews and just go see it. It will definitely be money well spent. Reading reviews sometimes gives away of the story (however little it may be)and ruin what would otherwise be nice little surprises. Best to go with a mind totally not knowing what the show has to offer. Did I say you won't be disappointed?