Hiccup (Jay Baruchel) has become a respected young man who's being tapped to replace his father, Stoick the Vast (Gerald Butler), as leader of their village. Conflicted, Hiccup takes to the skies with Toothless, where he and Astrid (America Ferrera) discover dragon hunters who think they're working with the mysterious Dragon Rider. The hunters are helping to build a dragon army for the vicious Drago (Djimon Hounsou), and Hiccup goes after him, determined to keep the peace.
Naturally, he meets the Dragon Rider, who is initially like Mononoke-hime but without the biting. This is where the animation truly shines -- the Dragon Rider moves with balletic, animal grace, in stark contrast to Hiccup's awkward mannerisms. There's one particular scene where the Dragon Rider dances from dragon to dragon as they fly. There's no dialogue, only music, but that sequence effectively shows two characters sharing a profound love for dragons, the sky, freedom, and seeing what others can't see.
The action and flight sequences are equally eye-popping. Everyone gets their share of the glory, including the secondary characters who are excellent as comic relief. Ruffnut (Kristen Wiig) is especially hilarious as the unimpressed gal being fought over by two dudes who ends up falling for the rippling biceps of the dragon hunters' leader, Eret son of Eret (Kit Harrington).
Hiccup's inventions are also fun--apart from his steering mechanisms for Toothless from the end of the first movie, he's made himself a couple of high-tech gadgets that work in a convincing manner. But what's coolest is Toothless, in a reveal that I'm convinced is a shout-out to Godzilla. Just like in the last movie, Toothless acts kind of as the Draco Ex Machina, but it's inspired by his loyalty and love for Hiccup.
How to Train Your Dragon 2 is a lot more grown-up than the first movie, and deals with themes like identity, responsibility, abandonment, commitment, control, and coexistence. Hiccup is the solid emotional core, particularly when he makes a discovery that sheds light on his distinctly non-Stoick characteristics.
TL;DR: This movie is in a class of its own in terms of animated movies of 2014. Watch in 3D.