Loosely based on the series of books by Cressida Cowell, the How to Train Your Dragon series has grown to become the jewel in the somewhat small and dusty crown of Dreamworks Animation. With Pixar killing it near enough year in, year out, the adventures of reluctant Viking leader Hiccup (Jay Baruchel) and his trusted Night Fury pal are the closest thing that Dreamworks have ever come to the quality and visual splendour of its most fearsome rivals. If you've kept up with the series since its debut in 2010, you'll have watched Hiccup grow out of his father's shadow into a battle-scarred warrior and forward-thinking frontiersman, who brought a close to his tribe's never-ending war with the dragons to discover the fire-breathing beasts actually make for useful and loving friends. The second instalment veered into incredibly dark territory, signalling a maturing tone that matched the protagonist's transformation from nervous kid to an innovator destined to change the lives of his people forever.

The third and presumably final entry into the series, The Hidden World, doesn't darken the tone further - it is still a kids' film after all - but you get the sense from very early on that we are heading inevitably towards an emotional parting of ways. Hiccup and his friends continue their quest to rescue captive dragons and bring them back to the village of Berk to live in harmony with humans. The problem is that they've become so good at their search-and-rescue missions that their home is now overcrowded with the lumbering beasts. Hiccup believes their only hope lies in 'the hidden world, a mysterious and possibly make-believe haven at the edge of the world spoken of by his late father Stoick (Gerard Butler). But cracks start to appear in the young chieftan's plans when his dragon and best friend Toothless happens across a Light Fury, the female of his species. Wild and distrusting of humans, the female bolts from Toothless' advances any time Hiccup shows his face to help, and it becomes clear that if he is ever to see his best bud happy, he must also let his dragon run free.

As ever, there's a dragon-hating antagonist to jeopardise Hiccup's plans in the form of renowned hunter Grimmel the Grisly (F. Murray Abraham), whose own mind-controlled dragons have the ability to vomit acid and melt pretty much anything in their wake. He certainly looks and sounds cool, but Grimmel shares much of the same motivation as the bad guys that come before him, and the character really symbolises the film's overall reluctance to dig that little bit deeper. For me, How to Train Your Dragon 2 really stepped up the game for this franchise, but it feels like returning director Dean DeBlois is happy to ease off the accelerator and ride this trilogy-closer out. If this were practically any other series, The Hidden World would be a delightful surprise, offering up great moments like the opening night-time raid and the sight of Toothless clumsily attempting win over his potential mate, the latter proving to be one of the most charming and heart-warming scenes of the entire trilogy. But with the knowledge of how great this could have been, The Hidden World is a disappointment, fizzling out with an ending that undoubtedly satisfies, but when compared to the emotional wallop of, say, Toy Story 3, plays it rather safe.