I saw How To Train Your Dragon last night. It was definitely cute and enjoyable. The characters were appealing and there was a lot of well-incorporated humor. (Astrid's intro scene, as a homage to cheesy action movies everywhere, particularly made me laugh.) I was especially impressed with the animation of the "lead" dragon and how the features go from looking menacing to looking puppyish ... with most of the work done by the viewer, not any actual change in the animation apart from facial expression.
One of the people I went with complained that the way they "typed" the dragons made it seem more cartoonish / childish, and after some thought, I have to agree. Sure, it's a kid's movie, but I think perhaps designing the dragon types in a simple way without funny names / powers would have enhanced the enjoyment of the film. My friend Amy (a flutist) and I sat there trying to figure out why Vikings had Scottish bagpipes.
And of course, this story has been told and told ... the misfit who shelters one of the enemy and grows to understand him is one of the oldest plots. There are a couple of surprises in how this is executed, but it's certainly not a model of unique plotting. It's still satisfying to watch. It's one of those stories that you know how it's going to come out and you still can't help engaging in it.
The 3D wasn't really necessary for this movie. There were a handful of gosh-wow applications (one with falling ash blurring out of the screen comes to mind) but most of the time, it felt like the animators forgot they had 3D capability. They stuck it in a couple places just for the heck of it. I wouldn't rush to see this one in 3D, in any case.