Take it from a lifelong fan of Arthur Conan Doyle: Robert Downey Jr. is so NOT Sherlock Holmes.
That's not a hindrance - in fact, it's a big help - as he and director Guy Ritchie bring Conan Doyle's dusty Victorian-age detective into the modern world.
Enough of the trappings are left in their action romp "Sherlock Holmes" - the lightning-fast cerebrations, the encyclopedic knowledge of London, the compulsive single-mindedness, the vain one-upmanship - to make Downey a reasonably faithful embodiment of the figure Conan Doyle created.
And of course, this is Downey, whose career resurgence rests on his ability to make the most unlikely role his own. He doesn't look like the classic Holmes, he plays the man as a scamp, he's after laughs as much as lawbreakers.
But Downey does a great Brit, he lives large in the part, and he brings a human spark to cold egghead Holmes that will help pack in huge audiences for a character on the fringes since the Basil Rathbone days.
Revisionists have done a number on Holmes before - he was psychoanalyzed by Sigmund Freud in "The Seven-Per-Cent Solution" and spoofed by Gene Wilder in "The Adventure of Sherlock Holmes' Smarter Brother."
So why shouldn't Ritchie put his London-rogues-and-rascals spin on Holmes and cast the detective into a brawn-over-brain action epic? After all, Conan Doyle's Holmes tales - particularly the novel-length ones - could be action rip-roarers.
The failing of Ritchie - and a team of four writers who share story or screenwriting credit - is the drab plot they built around Holmes, an uninspired tale of a secret society and potentially supernatural doings.
It's nonsense, a dumb Hollywood treatment that's beneath Holmes but is made watchable, even exhilarating at times, by clever chases and scuffles, a superb recreation of old London in its splendor and squalor, and the amiable interplay of the actors.
Jude Law heads the supporting cast as Holmes' colleague, Watson, less a loyal sidekick in Ritchie's creation than an odd-couple roomie in a bickering-buddy bromance.
Ravishing in every scene, Rachel McAdams was born to wear the sort of velvety, frilly Victorian garb she dons as Irene Adler, a cunning foil to Holmes as well as his romantic interest, the most-extreme revision by Ritchie and company.
Conan Doyle's Holmes was a monk who had no time or respect for women, save, in one thin story, a schemer named Irene Adler, the only woman who ever outsmarted him.
The literary Holmes admired Irene for her mind. Downey's Holmes admires McAdams' Irene for the whole comely package, and purists will groan over the puppy-dog caresses of Sherlock in love.
But did we mention that McAdams is ravishing in every scene?
Holmes' big mystery is the case of Lord Blackwood (Ritchie regular Mark Strong, who physically resembles Conan Doyle's Holmes far more than Downey). Hanged for a series of ritual murders, Blackwood won't stay in his grave, returning to terrorize London with an assault on Parliament aimed to bring him absolute power.
Skirting the fringes is shadowy Professor Moriarty, the criminal mastermind of Conan Doyle's tales, introduced here as Holmes' next great enemy for the inevitable sequel.
Eddie Marsan is perfectly cast as Scotland Yard Inspector Lestrade, the professional who deigns to let Holmes dabble in detection, happy to take credit when his amateur ally cracks a case.
The few playful put-downs between Holmes and Lestrade outshine the wall-to-wall discord between Holmes and Watson, the latter about to move out of their Baker Street flat as he prepares to wed Mary (Kelly Reilly, a strong presence in a small role).
Doubtless, the disharmony's there because you can't have an actor of Law's stature standing around forever marveling at Holmes' ingenuity.
But Downey and Law have a pleasant, wisecracking fraternity, Holmes the inspired headcase, Watson the stalwart comrade and caretaker. The story didn't need the artificial friction of their squabbling, a distraction in a film already heaped with distractions.
Ritchie piles on the excess. It serves him well in fashioning a dazzling, detailed version of 1880s London, with the pardon-our-dust construction of the landmark Tower Bridge a pivotal element.
The director should have toned down the manic, quick-cut style he honed on such modern crime tales as "Snatch" and "Lock, Stock and Two Smoking Barrels." Holmes was a quick thinker, but Ritchie cranks up his thought processes to such wink-of-an-eye speed that you begin to suspect it's meant to disguise the fact that no one is thinking much at all, at least when it comes to the story.
Anyone who wants their Holmes unsullied by revisionists has two great choices: the supreme 1980s and '90s TV adaptations of Holmes stories starring Jeremy Brett, an ideal incarnation of the detective as the author wrote him in those enduring Conan Doyle tales.
Who knows? Maybe the movie will make a few viewers go discover Conan Doyle for the first time.