NO SPOILERS
I really enjoyed this movie and I think it will eventually gain status as a cult classic someday. I think it requires more than one viewing to grasp all the nuances and one liners - which are hysterical. This movie is definitely not the typical homage to Barbie but instead humorously highlights the impact Barbie has/had on the socialization of young females (and males).
In the movie, Barbie is given the opportunity to visit the real world after experiencing some side effects (dark thoughts) she believes are from her human girl that plays with her. Barbie ends up meeting the Mom of the now grown human girl, who just happens to work for Mattel. Predictably the "real world" reflects male dominance in leadership roles whereas in "Barbie world" women hold the positions of power. Unlike some of the other reviewers - I didn't see it denigrating men and pushing a matriarchal agenda but rather illustrating how patriarchy does not really work for anyone. One of my favorite lines is when Ken (Ryan Gosling) reveals that once he figured out that patriarchy wasn't actually about horses, to his relief, he was no longer interested in it.
Highlights - there is an all-star cast and they are incredibly talented. Margot Robbie's physical stunts that mimic a Barbie doll are spot-on I usually don't like musical numbers in a movie, but the talented Ryan Gosling nailed it. Kate Mckinnon as weird Barbie was the icing on the cake.