I just saw it today. I don't want to spoil anything, so if you haven't seen the movie, stop reading this comment now.
The movie is dark. That's all. It's not like a cheesy, family blockbuster movie made just for the money. It's artsy, VERY well done, but dark. So, here's what to expect in the movie, yet again, there will be some spoilers:
It's pretty violent at times. At one point, the main wild thing, Carol, ripped off another wild thing's arm (sounds WAY more violent than it is, there is NO blood). Max doesn't have many friends, and for the whole movie up until the end, Max is very sad about his life. His sister ignores him.
The good things about the movie, though, is that it is very funny, humor that kids in the theatre laughed at loud about. What gets me mad about these comments, by the way, is that people are saying "Max doesn't really solve any of their problems", which is totally wrong. Max DOES solve his and the Wild Things' problems in the end. He rebuilds his relationship with his mother, and, even though he does get in a little fight with Carol, he is crying when Max leaves, and it's obvious that Max is still great friends with all of the Wild Things.
So, would I change anything about the movie? Of course I would. Is it a little violent and sad? Yes, it is. You have to know your kids and know if they could handle it. My 3-year-old cousin saw it w/ my aunt recently, and as they where leaving the theatre, he said "That was awesome!" Some kids might handle it differently, though. If you can't bring your kids, I suggest you go see it by yourself, because this is a great movie for adults as well.