Being immune nowadays to the cutesy antics that go on in modern American animated features, far preferring the more subtle (or more flamboyantly outrageous) Japanese equivalents, I found myself surprised by the quality of 'How to Train Your Dragon', a 2010 Dreamworks picture based on a popular British children's book series 'translated from the Old Norse' by Cressida Cowell. It did stunningly well for an animated feature, quickly grossing half a billion dollars worldwide, landing two Oscar nominations and securing for itself a solid spot in the IMDb Top 250. What's more, it's a great movie.

While there was much to praise about that film, its biggest cinematic success to my thinking was in successfully dabbling in a slew of genres while managing to avoid all the usual traps.

It was a fish out of water movie, following Hiccup, the young son of a Viking chief who's so different from the rest of his people that he could have been left with them as a changeling; he's not remotely Viking in size, temperament, intellect, even accent, as enjoyable as Jay Baruchel is in the role. It was a coming of age film, as Hiccup manoeuvers through the jeers and jibes to make his long suffering father proud by growing into his real talents. It was an animal movie, because those talents don't extend to killing the dragons which plague his village, but rather to making friends with them and eventually flying them into battle to bring peace to the small corner of the world that is the village of Berk.

Of course, 'How to Train Your Dragon' was also a romance, a fantasy, a comedy, an action flick, a period piece and a whole bunch of other genres to boot, but it worked well as each of them, aided by a strong cast of voice actors, a powerful score and a quirky set of dragon designs. This sequel retains all those boons and keeps all those genres in play, while adding yet another one to the mix, that of war movie.

Five years after this endearing dragon whisperer has saved both the Vikings of Berk from marauding dragons and those marauding dragons from the Vikings of Berk by transforming them all into allies, he finds himself newly tasked with saving both from a new and common foe, Drago Bludvist, magnificently voiced by Djimon Hounsou. He's a mad Viking warrior who has also found a way to bring dragons under his control but by dominating them rather than befriending them. He is a Viking, after all, and Hiccup aside, Vikings have a tendency to make their decisions with great big bloody axes. Naturally the two characters clash in a spectacular fashion, as do their wildly different philosophies.

Ironically it's Hiccup who brings Berk to Drago's attention to begin with because, as the film begins, he and his night fury, Toothless, are taking advantage of their mobility to explore a lot further afield than their formerly isolated village and they discover far more than they had planned. This irony provides strong emotional depth to the film, as Hiccup tries to dig his way out of the hole he's made for himself and his entire people. That depth is aided by the growing pains he's experiencing while fighting his father's plans to make him chief.

These early scenes are wonderful for their depth, their flair and for how much they highlight that this sequel is far from a rehash of its predecessor, immediately and bravely leaping far beyond that film's inherent confines to become something fresh and new. Writer/director Dean DeBlois has stated that he aimed to do to the first movie what the epic 'The Empire Strikes Back' did for the more insular 'Star Wars', an admirable goal.

He does succeed in making a real sequel rather than the usual rehash of what came before but in shinier paint, this being enjoyable both on its own merits and as a follow up. However, he's sadly unable to reach high enough to create the animated 'Empire' that he wanted. It's brought down in the end by its ambition, unable or unwilling to fill the sweeping scope that it opens up.

Sure, we're taken on dragonwing far beyond Berk but there are invisible elastic strings ready to snap every dragon back home when we start to realise that there's a world out there to see. In the end, we're not shown much of it, just a lot of sun, sea and sky, not to mention ice. We never see where new characters come from, so the centre of the universe remains the village of Berk and the brave new world remains tantalisingly over the horizon. For a film that aches to show us more than one little village, it's extremely reticent about actually doing so.

The story becomes rather like the map Hiccup has been compiling. He's been exploring further and further afield and drawing what he sees onto a gloriously patchwork map. Like that map, the movie lets us know that there are sights to be seen, but then folds them up so we can't see them and the story follows suit, similarly shrinks back down from the ambitious to the merely conventional. A half hour of delight, full of grand possibility, rollicking fun and the agreeable depth to back it up, gives way to plot convenience and wild inconsistency, eventually veering dangerously into predictable formula territory to become merely a good movie, not a great one.

I wonder how the sweep of it changed over time. While it sets itself up from the outset as a standalone movie unwilling to walk in its predecessor's shadow, I became gradually convinced that it was going to be the first half of an epic two part picture. It built so well, bringing in new characters and setting them onto decent story arcs, hinting at the action that would come and letting the story grow towards it at its own pace. Surely, this would leave us on a cliffhanger to be rescued by the third film, due in 2016, which would spend an hour and a half wrapping up the various strands of story in action-filled scene after action-filled scene. I believed that all the way to the finalé, when I realised that, no, they were going to wrap it up here and now and hey, it's done. That was acutely disappointing.

Don't get me wrong, there's still a lot to like but, unlike the first film, I'd be very surprised if this second one maintains its place in the IMDb Top 250 for long. As people rewatch and realise the glaring gap between what the film wanted to be and what it found itself willing to attempt, it will start to lose some of its shine. Hopefully the third movie will retain the ambition of this one but learn from its mistakes and avoid making more. Perhaps DeBlois is merely out of order. If this isn't this trilogy's 'Empire Strikes Back', perhaps it is at least its 'Return of the Jedi'.