Story sounded good in the trailers but when drawn out to the length of a movie, there were a lot of gaps and outright contrived places. I was sitting in front of a row of 8 tweeners and they thought the movie was great according to their comments afterward and their emoted noises during the film...I suppose the movie isn't really designed to do much other than attempt a few plot twists other than being mushy and sappy in spots. My wife enjoyed it which made it worthwhile I guess, otherwise I'd have rated it no more than three overall...
The 3D experience does lend a new sense of realism to what could otherwise be considered a cartoon. However, the story is excellent, the plot development is very good, and it's actually very difficult even for cynical people like myself not to shed a tear in certain places. The 3D effects, as others have stated, may startle the really little ones but overall it would be a great investment in an evening's entertainment for ages 5 to infinity...and beyond ;)