Went to see this movie in 3D (has gotten a LOT better since Toy Story 3), and this is one of those rare cases where the sequal is on par or better than the original. The voice acting is great, the story is great, the animation is incredible, and it always has something happening without feeling congested. My only harp on it, and it is minor, is that I wished Hiccup and Astrid had more interaction with eachother, but still just an incredible film! Has comedy, action, suspense, drama, even a bit of romance thrown in there and none of it feels forced. It flows really smoothly from scene to scene and emotion to emotion.
I give this movie a 9.5/10. If you haven't seen it, do, and the 3D really does it justice.