One 40 year old man's perspective -
Being an avid sci-fi/fantasy fan from an early age, I enjoyed the movie a lot, although I personally think the 3D effects weren't nearly worth the money they spent on them, and I do agree with people who feel it lacked originality.
I was much more concerned, however, about the impact the movie will have on my 10 year old nephew and his friends. Because this movie was rated PG, practically every kid is going to see it, at some point, which I think is a bit of a subtly-slid-in disaster for our culture. It's fairly clear to me that many, many modern single mothers are not really fully cognizant of the impact that sexual imagery (ie. nipple slips, nipples seen in shadows or through flimsy material, etc) and vulgar language has on young, developing male minds. No amount of talking, before or after, is going to reduce the impact. The idea that it will is a laughable misconception, imo, born out of the mother's need to reassure herself that she should be allowing what she's allowing.
My take: If, after careful review, you feel a need to reassure yourself - don't.