People were surprised when Bakshi said he was going to adapt The Lord of the Rings. This is after all the director of Fritz the Cat, Heavy Traffic and Coonskin. Nevertheless he played it strictly by the book and made a film to please even the purists. It would have been even better if he'd cut the last half-hour of faffing about at Helm's Deep, but it's still a strong, obsessively faithful adaptation that does things you wouldn't get from other directors and still stands up well today even compared with the Peter Jackson mega-busters.

I'll get the negative stuff out of the way first. It loses it at the end. We're so strongly invested in Frodo's quest to take the Ring to Mount Doom that it seems distracting and pointless for the narrative to meander off to Helm's Deep. Why should we care? So a bunch of rotoscoped spear-carriers are about to become Orc-chow... well, that's just too bad. Boromir thought it was a big deal, but Boromir was a loser. It's probably no coincidence that here the more obviously rotoscoped battle sequences start getting ever more badly integrated into the narrative, resulting in a last half-hour that's about 80% a confusingly edited waste of time and 20% cool stuff with Frodo, Sam and Gollum.

That said, there's still good stuff in there. Wormtongue is entertaining, as is any scene he's involved in. Gandalf's always value for money. The battle itself isn't bad. Nevertheless I regard this as an outstanding feature-length partial adaptation of The Lord of the Rings that's being let down by an additional half-hour appendix bolted on to the end.

It also doesn't really have an ending. It just stops, awaiting a Part Two that never came. It's only doing the first two books, which caused a massive fight between Bakshi and United Artists when they refused to call it The Lord of the Rings Part One.

At the end of the day though, Bakshi was simply sticking as closely as possible to Tolkien. He had a three million dollar script from John Boorman that he threw out because it had changed too much. He's even talked about how he stopped thinking about what Ralph Bakshi should be doing and instead got locked into a mindset of what Tolkien would have done instead, which shows you how hard he was working to be faithful. He certainly proved wrong anyone who'd been thinking this notorious X-rated animation director wouldn't have been able to do justice to the source material. On the contrary, he achieves some wonderful effects and in particular evokes throughout a sinister, oppressive mood. This cartoon is scary. The Black Riders with their red eyes are nightmare-worthy, the orks look like vampires and there's a level of realism that makes the film almost uncomfortable.

He did it with 100% rotoscoping, of course. They shot the whole thing in live-action in Spain, then turned that into animation. This makes for alarming discontinuities of style, but this is Bakshi we're talking about and its brazenness makes it work. The only surprise is that he didn't include raw live-action sequences. The result was easily the longest feature-length animated film ever made up to that time, plus of course there's something uniquely horrible about watching a cartoon in which undead monsters from hell are also, obviously, real. They're in a cartoon, yes, but at the same time we can see we're looking at real people on real horses. Usually the main characters will be fully replaced with hand-drawn equivalents, but battle scenes and other busy shots (e.g. the inn) are only the equivalent of a Photoshop filter away from photorealism.

This apparent clash works far better than you'd think, only falling down on the rare occasions when Frodo or Gandalf go from one style to the other. I liked it a lot and I think it makes the movie what it is.

The only design element that doesn't work is the elves. They're a bit naff. If you're hoping for Orlando Bloom, think again. However the hobbits are great, especially ugly fat-faced Sam and his barrage balloon nose. The Black Riders are terrifying. Moments like that crow flying up at the beginning are way more sinister than they have any right to be. Saruman's magic trap is a simple effect, but it looks extraordinary. Visually, this is a marvel.

Of the characters, I liked best the hobbits. Frodo's purity comes across strongly. "And I came to test you!" Sam gets gay subtext, most noticeably where he squeezes Frodo's shoulder as they listen to a love song. Gollum's obviously wonderful, although it's a bit of a stretch calling him a hobbit by this point in his life. Finally Bilbo gets more weight than I remember him as getting in the Peter Jackson version and so among other things, this film comes across as sincere and deeply respectful towards the story that preceded it, The Hobbit. I appreciated that. I've always liked The Hobbit. "Don't adventures ever have an end?" is so sad, by the way.

It's full of British accents and actors. The most famous names here are John Hurt (Aragorn) and Anthony Daniels (Legolas) on one of the few occasions when he's not C-3PO, but Doctor Who fans will recognise plenty of other names too. Gandalf is William Squire (the Shadow in The Armageddon Factor), Frodo is Christopher Guard (Bellboy in The Greatest Show in the Galaxy), Pippin is Dominic Guard (Olvir in Terminus), Elrond is Andre Morell (Marshal Gaspard de Saux-Tavannes in The Massacre), Galadriel is Annette Crosbie (Mrs Angelo in The Eleventh Hour) and there's an innkeeper who also played Mr Forrester in Planet of Giants.

It's incomplete, of course. It needs a sequel that Bakshi never got to make, although goodness knows why. It can't be for lack of money, since this film took more than 30 million at the box office on a budget of 4 million, while it can't be for lack of critical success since it was nominated for a Golden Globe. However the year before, NBC had shown an animated TV special of The Hobbit and so in 1980 the same team released their own unofficial TV sequel to Bakshi's film. You can buy all three in a boxed set, although of course it's Bakshi's movie that everyone remembers.

Overall, it's excellent. It falls down in the final act, but we've had enough great stuff by then that I didn't mind, while in any case... well, it's Tolkien. They even do Tolkien songs and dialogue that's in Sindarin. The rotoscoping gives it realism and weight, but at the same time there are cartoonish bits I really enjoy. I liked Treebeard's cameo, for no particular reason. I hadn't been expecting him, although I don't know why. Well worth a spin and, in its way, much more creative than the Jackson versions. It's powerful.

"My sister-daughter Eowyn." I presume that's not what it sounds like.