PROBLEM SOLVERS:Watson (left, Jude Law) and Holmes (Robert Downey Jr.) puzzle over their latest mystery.

THERE ARE moments during Sherlock Holmes when you wish you could hit director Guy Ritchie with his own storyboard; there are bone-crushing fights that you feel like applauding just to celebrate the fact that they're over at last. Yet all in all, Sherlock Holmes is ripping fun. Robert Downey Jr.'s expert acting reflects William Blake's thought that if you could open the doors of perception, you would see the world as it is: infinite. This insight sums up the mind of the great detective—it also sums up the mind of a schizophrenic.

Downey's performance seems to be based a little on Nicol Williamson's nervous-breakdown sufferer in The Seven-Per-Cent Solution, but there's less of Olivier in Downey's performance than there was in Williamson's, less raising of the voice to let it ring off the proscenium arch. Downey's schizoid man arouses a note of pity for his own solitude and, at the same time, admiration of his infernal speed. There's a note of a scandalous Bohemian in Holmes when he's cleaned up, something of the Pre-Raphaelite decadent in him. ("Ah, putrefaction," he says, flaring his nostrils at a clue.)

He is certainly gratifying to look at. When on his game, Downey's Holmes is a dandy in high Victorian regalia, smoked glasses, ascots and the kind of slanted hats worn in Oscar Wilde's circle. But we also see another side of Holmes—a hermit crab in a dank flat, huddled under a dressing gown so raveled it looks as shaggy as a bear skin. The film's saddest moment comes when an anxious Holmes can't let his stream of deductions stop when meeting Watson's then-girlfriend Mary (Kelly Reilly). It's compulsive observation as a kind of OCD.

Ritchie follows the sturdy paradigm of one of the best Holmes movies, 1939's The Adventures of Sherlock Holmes, from a horse-drawn coach race at the start to the fight on a towering London monument. Mark Strong's staring and broad-faced Lord Blackwood—a Victorian Aleister Crowley—is apprehended by Holmes in mid–black mass and ushered in to a well-deserved hanging. "You and I are bound together," Blackwood promises Holmes before he takes the last drop.

Naturally, Inspector Lestrade (a beautifully cast Eddie Marsan, looking more like a bull terrier than ever) decides that the case is closed. But it seems the grave cannot hold Blackwood: we cut to a family tomb that looks as if it had been blown apart from the inside. In the meantime, Holmes is approached by two different clients: the ever-troublesome Irene Adler (Rachel McAdams, decorative but dull) and the head of a Masons-like group, who are troubled by the specter of Blackwood.

Ritchie's now-traditional fast-forward and fast-rewind techniques are used cleverly to revisit crime scenes: a little something for all of us who see but fail to observe. The stopping points include horror laboratories, a steam-powered abattoir, deadly copper bathtubs and spontaneous immolation. The look has more to do with David Fincher than Basil Rathbone.

And yet the muddy streets and bad teeth aren't an unviable idea: Ritchie's Cockneyfying of the adventure gives it some fresh texture. The movie keeps coming back to a serene partnership—when Holmes says, "The game's afoot," Jude Law's formidable Watson picks up the rest of the Henry V quote.

Sherlock Holmes' CGI animation is sometimes impressive; one Thames-front scene seems to go back into the frame for miles. Too bad the backdrop in the final fight scene is far more indifferent. Ritchie struggles with the usual problem of trying to illustrate the kind of public panic that would occur if the Antichrist were to rise and stalk London. Only a few agitated picketers cross the screen. Compare the aimless hubbub to the thrifty effectiveness of Fritz Lang establishing the same sense of civic emergency in M.

The big explosion—a slow-motion jump in front of a flaming green screen—is a custom that needs to die right now. With luck, this will be the final nail in its coffin. A nude scene is one deficiency of taste. So is a hulking French giant brawler who keeps turning up, as remorselessly and to as little purpose as Richard Kiel in the lousiest Bond movies.

Ritchie filches a line from The Terminator to lead us into the sequel. We see where it's headed; we have a few satisfactory visions of the Napoleon of Crime, seated in corners of trains and carriages. These visions are much more like Lang: Professor M. is portrayed as an apparently untenanted suit of black clothes, gleaming gloves and top hat, with a tell-tale smudge of blackboard chalk on the lapel. Bring him on. Sherlock Holmes rattles our cages with superstitious craziness, then turns into a celebration of pure reason, unique in a season of movies meant to leave your brain in a molten puddle of crypto-religious awe.

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SHERLOCK HOLMES (PG-13; 128 min.), directed by Guy Ritchie, written by Michael Robert Johnson et al., photographed by Philippe Rousselot and starring Robert Downey Jr. and Jude Law , opens Dec. 25.