While I haven't seen all the DreamWorks animated features, I've seen most of them. How to Train Your Dragon is my favorite so far. While I enjoyed Kung Fu Panda, I didn't find Po's transformation from loser to warrior convincing. The arc for Hiccup, the boy pictured above, is better constructed and the plot points are all in place.
The story has elements of E.T. and is pretty predictable, but it is well told and emotionally satisfying. There's a good balance of humour and suspense. The film is built on a father-son relationship that works within the context of the film and resembles Disney's Chicken Little. The dragon designs are nicely balanced between caricature and menace and the Vikings are fun to look at.
There are things that I could criticize in the film, but they don't detract from the overall experience. I saw the film flat, not in 3D, as I was more interested in judging the story elements than I was the technique. I still found the camera moves too busy in the early part of the film and wonder if I would have suffered whiplash had I watched it in 3D. The children, except for the male and female leads, are one dimensional, which often happens with supporting characters in animated films. It's a bit of a stretch to have Vikings talking with Scottish accents, though I guess it is plausible. The relationship of the largest dragon to the others is not clear and probably unscientific. I can't say more without spoiling something.
I couldn't help thinking while watching the film that should it outgross Disney's Bolt (and it deserves to), it will be vindication for director Chris Sanders, who was removed from the Disney film by John Lasseter. Dragon also seems to me to be the DreamWorks film most dominated by it's directors (Sanders and Dean Dublois). With DreamWorks now set on releasing 5 films every two years, I think it would be all to the good for Jeffrey Katzenberg to loosen the reins a little and let directors put their stamp on films.