This is a Holmes so at odds with our usual movie concept of him (and of Watson) that you have to change your thinking about the characters. I've just been reading the Christianity Today review which points out that the two characters as played here are actually much more like the original Conan Doyle protagonists than the way they've been portrayed in many other movies.
Doyle describes [Holmes] as "eccentric" and "bohemian"—both perfectly describe this new portrayal. In one scene, Holmes seems to use a hallucinatory drug to gain insight into his enemy's plan—also consistent with Doyle's depiction.
Watson here also differs from his traditional Hollywood portrayal. Doyle's stories never depicted him as the portly, befuddled sidekick; he's originally described as a veteran of the Afghan war, thin, strong, and packing a revolver. Yes, he's a foil to Holmes' intellect, but more as an intelligent everyman for the detective to play off, not merely for comic relief....
Well, there you go. I knew Holmes had an eccentricity about him, but wouldn't have thought of him as the 'wild man' Downey portrays here. Watson is certainly contrary to any previous depiction - his limp comes and goes (I wasn't sure whether it was due to his career as a soldier or the innumerable fights he gets into during the movie), and while I knew the names of Lestrade, Hudson and Baker St from the back of my trivia-filled brain, I'd never heard of Irene Adler or Mary Marstan.
So that rather undercuts some of what I was going to say about the movie. Holmes may be closer to Doyle's version after all - though he never gets to play the violin in this movie. He plucks at it in a seemingly absentminded way, but never goes into full flight - there's not even a bow in sight (though given the absolute clutter in his flat that's hardly surprising).
Taking the movie, therefore, on its merits we have the following:
- a solid storyline (we don't get the explanations of several features until almost the end)
- frequently frantic pace
- banter along the lines of many other Hollywood male partnerships (think Butch Cassidy and the Sundance Kid)
- superb renditions of a period London done in incredible detail (presumably with the help of considerable CGI)
- heart-thumping music by Hans Zimmer (we were right beside one of the speakers and the violinists' bows were almost whipping our ears off)
- excellent cinematography by Philippe Rousselot (read the list of his credits and you'll have an idea of his style) in which the camera sits still only when necessary
- an almost method-acting approach to Holmes by Robert Downey Jnr, which just manages to avoid the absurd
- an intriguing storytelling approach by Guy Ritchie in which we are sometimes see the action before it happens, sometimes have a few moments of flashback to bring us up to speed, and all the time have to rely our wits to keep up with the manic way films are made these days - no wonder we think older movies are slow.
Put your preconceptions about the characters aside, and you'll enjoy this thoroughly.