It was awesome. This is an excellent kids movie. It teaches a lot of important lessons like using your head, and avoiding stereotypes without beating you over the head about it. It also has a fascinating mythology to the whole thing that is pervasive but comes nowhere near overwhelming anyone unfamiliar with the setting (and I certainly wasn't going into this.)
The summary of the story is that a child named Hiccup doesn't fit in with the rest of the village of Vikings that are routinely raided by Dragons. Obviously (since the title kind of gives it away) Hiccup ends up with a dragon that he has to deal with and bonds with it. The rest of the movie involves how Hiccup solves the challenges that brings him, including how to rectify being the friend of a dragon amongst a people that hate dragons and want to kill them on sight.