A good, well-meaning theme that's undermined by a combination of its own hasty, badly timed follow-through and viewers feeling that their vague expectations were not met. How ironic.
I think the biggest shortcoming of this film was that it tried to do too much and went in too many directions. Pixar tried to please everyone and wound up pleasing no one. Elements of Disney princess fairytale, dark fantasy, a realistic family dynamic with a side of wacky humor and cheap movie monster were thrown in a blender. With the glut of recent movies with fantasy and archery themes (How to Train your Dragon, Hunger Games, etc.), sheer bad timing makes everything feel overdone. Everyone was distracted from what they wanted to see by the things that they weren't going to the film for.
BUT if you can get past these most glaring flaws, its still a solid film.
At its heart is the relationship between mother and daughter. The film tries to make flawed, likable characters in the heroine and her mother, but everyone's just going to wind up feeling far more sympathy for one character than the other. As an example, Merida gets out of her arranged marriage without breaking the originally agreed upon rules in the archery contest which is great, but she does it in such a disrespectful way that she risks starting a war between four kingdoms which isn't fair to anyone else. It can come off as a totally awesome move by an ass-kicking rebellious princess, or a massively selfish one by a spoiled royal brat.
You know what, call me cynical, but this sort of ambiguity is kind of hard for North American audiences who are more accustomed to 'clearly defined us vs. them, righteous hero kicks nasty villain's ass while we cheer' type of thing. I think they might have been able to work out some of these issues if they had lengthened the film a bit, but there's no way we'll ever know now. Overall, its not one of Pixar's best, but still a well done, unique, enjoyable film. I applaud their efforts and I'm betting critics will be easier on it in the years to come and that it will be better received overseas.