The end of a saga, whether an epic poem, a novel or a film, can be a painful experience.

Sometimes it involves a sense of loss when it’s all over; sometimes disappointment that what started so well ended so feebly. Film franchises, in particular, tend to weaken the longer they go on.

But when the ending works, trepidation and pain give way to euphoria. That’s how it was with the final instalment of The Lord Of The Rings; and that’s how it is with the conclusion of the Harry Potters. Not only is the eighth Potter film a fitting summation of a decade of careful plotting and character development, and an emotional farewell to cherished characters, it’s also an incredible film in its own right. Indeed, alongside Alfonso Cuaron’s atmospheric and impeccably acted third instalment (The Prisoner Of Azkaban), it is the best of the series by far.

But the first part of Deathly Hallows did not bode well. As the loose ends started to be gathered, the effect felt downbeat and disjointed. The series’ first departure from Hogwarts left the principal characters – Harry (Daniel Radcliffe), Ron (Rupert Grint) and Hermione (Emma Watson) – horribly exposed. As they wandered, alone and despondent away from their beloved school, the film plummeted into gloom. One can see now that director David Yates and the indefatigable Potter adaptor Steve Kloves (who has written all but one of the films) were simply putting their pieces into place for the final battle, biding their time and saving their best for last. Part 1 was the lull before the storm.

And the finale is an unrelenting, edge-of-your-seat hurricane of action and drama. As Harry comments to his chums at the outset: “When do our plans actually work? We make a plan, we turn up, and all hell breaks loose.” The evil Lord Voldemort’s final assault on Hogwarts will seem a lot like hell, to those defending it. What Harry doesn’t say is that the trio usually escape unscathed; one of the most satisfying aspects of this finale – for those few, at least, who haven’t read the book – is that this time their safety is far from assured. Enough fine characters have already died for us to know that this is, for a few more, a fight to the death.

Yates announces his intention to go out with a magnificent bang in the very first shots, unveiling the series’ first full use of 3D. As spooky Dementors float over a darkened Hogwarts, and the cameras zoom in on Professor Snape (Alan Rickman) brooding on the parapet, the technology is impeccable, the effect immediately foreboding.

We cut to the beach where the loyal elf Dobby lost his life at the end of Part 1. “I need to talk to the goblin,” declares Potter, the maturity and force of his demand an indication of how much he has grown up since he was first whisked away to Hogwarts, a wide-eyed, innocent boy. In fact, the trio of friends stopped being kids, in any normal sense, a long time ago; and just as Harry, Ron and Hermione are now such accomplished wizards that we take each new, powerful spell as a given, not the novelty it used to be, so Grint, Watson and (especially) Radcliffe have grown enormously as players. In particular, their gravitas is the anchor of Deathly Hallows.

The aforementioned goblin is the key to the kids’ search for the Horcruxes – pieces of Voldemort’s soul, which he has hidden to secure his immortality. The film is effectively a race: Harry and friends must find and destroy the Horcruxes before Voldemort lays waste to Hogwarts.

What follows includes a marvellous sequence with a dragon (the 3D again flexing its muscles, as the beast rumbles over rooftops, the kids clinging to its back) and an extraordinary battle scene – not of the calibre of those in Lord Of The Rings, but ambitious, well-staged and surprisingly vicious, involving wizards, ogres, giant spiders and Voldemort’s destructive ire. Those merry games of Quidditch seem a long, long time ago.

Certain characters have their moment in the sun, not least Maggie Smith’s divine Professor McGonagall and Julie Walters’s Mrs Weasley; others, such as Michael Gambon’s Dumbledore and Gary Oldman’s Sirius Black have potent cameos from beyond. And Rickman’s Snape has a resolution as shocking as the series’ most ambiguous and fascinating character deserves.

But what we’ve really been waiting for, all these years, is the final confrontation between Harry and Voldemort, the orphaned innocent and the blackest of villains. In large part, the expectation has been for the moment when Ralph Fiennes – his physical presence no more than a wisp in the earlier films, growing more tangible as the series has progressed – could fully strut his stuff. He doesn’t disappoint, finding incredible nuance – hatred, anger, frustration, fear and magnificent malice – within that chilling, snake-like face. Radcliffe, doughty as ever as he stares death in the face, is a worthy match. Together they provide this fine series with a truly fitting climax.