So it's surprising that The Two Towers is the closest the Lord of the Rings trilogy comes to faltering. It's not a weak instalment by any means, and by most standards it's probably a five-star film, but the multiple plot strands and meandering structure keep it slightly below the impossibly high bar set by the films on either side of it.
In contrast to Fellowship's tight-knit ensemble and pacy, linear plot, Towers is a much more scattered and uneasy story. The Fellowship is broken, and nobody's future is looking too bright: Frodo and Sam are off on what's essentially a suicide mission to throw the ring into Mount Doom; Merry and Pippin are captured first by Orcs and later by a tedious plotline (more on which later), and Aragorn, Legolas and Gimli fight to defend the troubled kingdom of Rohan from an invasion by dark wizard Saruman and his creepy, ugly army.
So there are three stories going on in The Two Towers, and only two of them really work.
Looking at the pitch for Merry and Pippin's strand, it's not hard to work out why. Two likable but essentially lightweight (at this stage) characters are rescued from capture by a giant, ancient tree creature, and spend the rest of the film making reaction faces while he speaks very, very, very slowly.
Treebeard is just one of those characters who works better on the page; effects-wise he's handled perfectly well, but the film literally and figuratively slows down every time the C plot takes centre stage. If you're doing a Lord of the Rings all-nighter, as we at DS have been known to do on occasion, these scenes are your opportunity to take a nap.
Frodo and Sam's jaunt through Mordor, though, makes for gripping and worrying viewing from the start, thanks in large part to Andy Serkis's mesmerising debut as Gollum - his first multiple-personality meltdown remains a trilogy high point. There's a creeping sense of dread, too, in the progression of Frodo's character, as he begins to feel the corrupting influence of the ring. Elijah Wood continues to be a compelling lead as his wide-eyed bravery shifts subtly into something darker, and he's complemented by a touching Sean Astin as Frodo's loyal, increasingly concerned manservant/best friend/platonic life partner Sam.
But the bulk of The Two Towers is given over to the faceoff between Rohan and Isengard, and specifically to Viggo Mortensen's Aragorn whose arc becomes quasi-biblical. Initially reluctant to accept the leadership he's plainly suited for, Aragorn dies, is reborn, and returns triumphantly on horseback just in time to head up the stand against Saruman at Helm's Deep.
It's one of the few instances of Peter Jackson and his co-writers creating an entirely new section of story that's nowhere to be found in Tolkien's text at all, and it works spectacularly well. With Frodo increasingly succumbing to fear and the ring's moral corrosion, Aragorn becomes the trilogy's moral centre and Mortensen's emotionally committed turn allows him to be both noble and flawed.
Aragorn also gets a female admirer in Eowyn (Miranda Otto), who falls in love with him in the space of roughly 15 seconds, but we're not questioning the logic of this. One look at this picture should show you where she's coming from.
And come the third act, any misgivings about Towers' structure will be long forgotten, swept away in the sprawling, genuinely epic set piece that is the Battle of Helm's Deep. The groundbreaking motion-capture technology used to bring Serkis to life as Gollum overshadowed many of the series' other CGI innovations, but the artistry of Weta Digital comes through just as impressively as the two warring armies gather to do battle - the sense of scope is breathtaking.
Another significant change from the book was making Helm's Deep the climax (Tolkien had the giant spider Shelob as his closing note), and it's another smart decision in cinematic terms, allowing for a real sense of payoff in a story that otherwise threatened to tail off rather than conclude.
We can't let this review pass without mentioning that The Two Towers also spawned perhaps the two finest Lord of the Rings song-based internet memes: 'They're Taking the Hobbits to Isengard!' and 'The Potatoes Song', and for that alone it gets the final star.
It's darker and more downbeat than Fellowship, and resolves in a way that seems to deliberately leave you uneasy rather than fulfilled, but as character-rich, thoughtfully plotted adventure drama, it's peerless.
Gallery - The Lord of the Rings trilogy in pictures