Anyone who was entranced by “The Fellowship of the Ring,” the initial installment of Peter Jackson’s adaptation of J.R.R. Tolkein’s much-admired trilogy, and who might be apprehensive about whether the second film will measure up to its predecessor, can breathe a sigh of relief. “The Lord of the Rings: The Two Towers” is a majestic achievement, an epic of astonishing grandeur and surprising emotional depth; meeting, even exceeding, expectations, it’s the best sequel since “The Empire Strikes Back.”

Like that second “Star Wars” film, this one is, in many respects, an improvement on the first. While it can’t recapture the sense of freshness and innocence that “Fellowship” possessed, it makes up for the loss by being smoother, less episodic and on an even more massive scale. Opening in medias res, without wasting time recapitulating the previous episode, it also resembles “Empire” in its exquisite juggling of different plot strands as it follows various groups of characters along their separate routes. Most important to the ultimate outcome of Tolkien’s tale, of course, are Frodo (Elijah Wood) and Sam (Sean Astin), who continue their journey toward Modor to destroy the titular ring to keep it from the grasp of the evil wizard Saruman (Christopher Lee); along the way they become involved with the emaciated, Uriah Heepish creature Gollum (performed by Andy Serkis and then radically transformed in appearance by special effects) and eventually with the head of Gondor’s forces, Faramir (David Wenham), who believes that the ring could give him the power to withstand the forces threatening his realm. Meanwhile the other pair of hobbits, Merry (Dominic Monaghan) and Pippin (Billy Boyd), escape from a hostile army into an enchanted forest, where they’re literally taken up by Treebeard (voiced by John Rhys-Davies), a huge, lumbering “tree shepherd” who (which?), along with his equally mobile colleagues, must decide whether to take part in the war over Middle Earth. Third, there’s the courageous trio of Aragorn (Viggo Mortensen), Legolas (Orlando Bloom) and Gimli (John Rhys-Davies again), who travel to the realm of Rohan to aid King Theoden (Bernard Hill) and his beauteous niece Eowyn (Miranda Otto) against Saruman’s serpentine henchman Wormtongue (Brad Dourif) and the wizard’s enormous army–an effort that takes them all to the vast fortress of Helm’s Deep. Eowyn, one notes, takes a distinct interest in Aragorn, though he constantly recollects his feelings for the absent Arwen (Liv Tyler). And lastly Gandalf (Ian McKellen) returns, transformed from grey to white as a result of the battle in which he’d apparently died in episode one, to assist various of the heroes at critical junctures.

With this wealth of characters and incident, it’s amazing that Jackson, along with co-writers Fran Walsh, Philippa Boyens and Stephen Sinclair and aided by superlative editing from Michael Horton and Jabez Olssen, keeps all the plot threads so wonderfully clear and the interrelationships so effectively drawn. He manages to give the film spectacular breadth while moving the story along briskly, and his handling of the big combat sequences seems more assured than in the previous film. A good deal of the credit must also be directed toward the large design team, which has fashioned some very evocative sets and costumes, and the even larger effects crew, which not only works wonders in the huge battles which make up much of the picture’s final act but has manufactured a slew of memorable creatures as well. Treebeard and his companions are witty and strangely haunting entities, for example, and flying dragons and gruesome buffalo-like beasts, as well as the grim enemy soldiers who use them as steeds, are also imaginatively rendered. The masterpiece, though, is surely Gollum, who looks like a cadaverous version of Peter Lorre, with huge, bulging eyes, scraps of stringy hair and a sallow, grey complexion. He also turns out to be suffering from multiple personality disorder, and occasionally has debates with himself–switching between the duplicitous schemer who prattles on about recovering “my precious,” as he calls the ring that’s reduced him to his present state, and the frightened, obsequious servant who pledges his loyalty to Frodo in his quest. (It’s the same device that Emily Watson employed in “Breaking the Waves,” but here it works far better, because it’s meant to be grimly humorous.) Gollum, quite simply, succeeds where George Lucas’ attempts to fashion viable CGI characters have so miserably failed (Jar Jar Binks being the most obvious example); he (it?) proves conclusively that a computer-generated figure can possess the same sort of emotional impact that traditional animated ones have often had in the past. There’s also a good deal of wit in his portrayal: watch for the moment when, grabbing the sides of his head with his hands in a fit of terror, he looks almost exactly like the famous image in Edvard Munch’s “The Scream.”

Compared to Gollum, even McKellen as the transfigured Gandalf seems a bit ordinary, but he again brings a welcome measure of Guinness-like (or Obi Wan-like) gravity to the good wizard, just as Lee once more invests Saruman with his patented silken malice, even if the role has been considerably trimmed from the last installment. Mortensen and Bloom carry themselves as heroically as ever, and Rhys-Davies injects much of the humor in the piece (apart from the darker smiles associated with Gollum) in his twin roles as the vertically-impaired Gimli and the oracular Treebeard. Wood and Astin make a good pair, even if their roles here are less central to the action than one might expect (the episodes in which they’re involved are uniformly dark and bleak in tone, as well), and Boyd and Monaghan still cut pleasantly leprechaun-like figures. On the distaff side, only Otto has much opportunity to make an impression, and she’s fine; Tyler and Cate Blanchett, as Galadriel, are reduced to little more than cameos. Less successful are the Rohan duo of Hill and Dourif, the former never quite filling the monarch’s legendary boots and the latter oozing a bit too much oily villainy of the kind he’s peddled in all too many direct-to-video titles. On the other hand, Wenham cuts a fine figure as the ambiguous hero of Gondor.

Topping everything off is the sumptuous cinematography of Andrew Lesnie, which captures the New Zealand locales to often breathtaking effect, and Howard Shore’s rousing score, which underlines the action splendidly without getting intrusive about it.

“The Two Towers” also resembles “The Empire Strikes Back,” of course, in ending without a full resolution, and it doesn’t boast the sort of startling revelation that gave the close of Irvin Kirshner’s film such punch. But Jackson has once more done Tolkien’s original up so well that the only disappointment most viewers will be feeling, even after 179 minutes (which, admittedly, don’t seem anywhere near that long), is that they have to wait twelve months for the next helping.