I found this to be a good laugh, once I'd tuned into Downey Jr's mumbling (why do they do that? Why? I'm going to buy the DVD anyway, but not just so that I can figure out the dialogue). I'm not too familiar with the books - I think I got bored partway through A Study in Scarlet when reading my copy of The Complete, though I can't be bothered to check - but I recall Holmes being a singlestick expert, and ACD is famous for introducing (and misspelling) Bartitsu, so the fight sequences fit, here - including Holmes indulging in such things recreationally. The concept of drug addiction is cranked way down, though.
The plot is rather silly, being basically Voldemort, and Rachel McAdams's raison d'etre is attached with a staple gun, but never mind.
As far as interpretations go, there are shades of Jonathan Creek, but then, JC's a modern interpretation of Holmes anyway. But there's a massive, overcast shadow here, which is Hugh Laurie's House. Downey Jr's portrayal (and Johnson et al's writing) ignore the Rathbonesque stiff upper lip, and revel in Holmes's selfish obsession, playing it for (poor) laughs in some cases, but since House has already done six seasons of that, this does feel both behind the times and cannibalistic. But Christ, it would have been good to see Hugh Laurie in this role...
Jude Law does okay as Watson, long-suffering, aware of
Rachel McAdams, as Irene Adler (is that a character from the books? I dunno), starts well, but her character is somewhat dismantled deliberately by the writing as the film progresses. She's described as someone who has outwitted Holmes twice before, yet gets written into a the Damsel In Distress corner. Lazy - they could have fixed that scene so easily.
But maybe they were busy fixing something else: watch the trailers again: all of McAdams's appearances in the trailers are in a scene that's been cut from the movie, and quite possibly replaced with something else (the one with the bottle). I can guess why, too, but it's interesting.
Oh, and I liked the homage to the watch scene from the first book, when Watson first meets Holmes.
London looks reasonably good, although there are strange disconnects between the CGI-esque fairytale Dickens Gothic streets, all black and blue shading, and the footage of, say, a barge on the Thames outside the Palace of Westminster; it's like stepping from Lemony Snicket into James Bond.
But, overall, pretty good. This is a Guy Ritchie film, remember. Set in London. It so easily could have been so much worse.