I really liked this movie. I've watched it at least twice, since I ended up wanting to revisit it as an adult after having watched it as a child.
I think the cast of characters is really funny and interesting; I love how Hiccup developed as a character - gaining confidence as he became more comfortable around Toothless - and how the other characters recognized that he changed and accepted him.
The soundtrack is also really good, especially that one song that plays when Hiccup flies for the first time - it's called Test Drive.