I find it interesting this is basically a story of how a woman becomes huge and powerful and decides not to get married to prat. It is a kind of feminist reimaging of Attack of the 50 Foot Woman where a woman is likewise effected by an alien to become huge and powerful, and ends up killing herself and her unfaithful husband. In this new version Susan decides not to marry her selfish potential husband at all, and goes off to become a kind of superhero. A much better ending.
The previews are rather coy about the actual themes of the movie, playing up the jokes and slapstick. This may well be wise from a marketing perspective, and there is enough laughs and explosions to make any kid (and undemanding adult) happy. But I, for one, am thrilled to see the underlying story arc of this movie--and an honest-to-goodness female hero in a kid's movies aimed at both sexes.
(And the 3D also rocks.)