The first 15 minutes of the movie made me cry, and are as emotionally affecting as anything I've seen at the movies this year, animated or live-action. And it sets up several simple moments with huge emotional pay offs before the movie is done. The story itself is sweet, a little silly, and a lot of fun. The 3D isn't eye-popping things coming at you, it just adds to the depth of the animation in lovely ways.
Go to see this movie, and see it in 3D if you can. The two hours you spend will be worth the sweetness and joy you walk away with.