It was, to put it mildly, fantastic. It looked amazing, it sounded amazing, it was touching, funny, exciting, and damn near perfect in every way. The biggest criticism I can think of is that the water looked too good. In that it looked like real water rather than cartoon-CGI water. Oh, and it falls possibly too squarely into the box marked "Boy who feels different to everyone else learns to do things his own way rather than fit in and thus (a) gets girl, (b) kills baddies, (c) saves entire planet*." Still, ranks up there with "Cloudy with a Chance of Meatballs" as far as quality and fun levels go.
Julie and I wandered most of the way home talking about how fucking much we want a dragon. Which, considering neither of us is usually part of the dragon squee club is pretty impressive.
Oh, and the 3D was utterly seamless for me. I ceased to notice it for most of the film, and things just looked "realer". Which was great, because the scenery was damned impressive.
See this, you won't regret it.
*That's a metaphor and a PWEI reference. There is no literal planet saving in this movie. There are, however, dragons.