The plot features Lord Blackwood, an aristocratic black magic type. Holmes prevents him from sacrificing a young woman, and sends him to the gallows. He promises revenge from beyond the grave, but Watson pronounces him dead. I'll save the spoiler for the end.
I can see how they got the idea for Downey as Holmes. He's a lovable bad boy like Tony Stark, with the disguise skills of Kirk Lazarus from Tropic Thunder. I generally liked his Holmes, but I have a few reservations:
- This Holmes was a bit of a Bohemian dandy, wearing colorful ascots and artistic collars when he wasn't wearing linens and braces. I know Holmes was a sharp and eccentric dresser, but I don't see him as Oscar Wilde
- I couldn't shake the impression that it was Hugh Laurie playing Holmes. Since I don't watch House, I didn't get the connection. But I guess Laurie's House is a Holmes tribute, so that makes sense
- The greatest Holmes ever casts a shadow over every other performance: Jeremy Brett
I like the younger, more vigorous, more brutal Holmes and Watson. It's similar to the James Bond re-boot. Holmes is still as intellectual as ever, but is not purely a thinker. The Canon clearly shows that he is also a brawler, a master of disguise and a dabbler in narcotics. (They tone down the drug use in this movie, but cocaine is implied.)
Irene Adler, played by Rachel McAdams, is also in the Canon, although she is more popular with the post-Conan Doyle writers. She gets a good role here, but the real romance is between Holmes and Watson. Holmes' continual attempts to sabotage Watson's marriage is a running gag throughout the movie. I hate to call this a "bro-mance", but...
So, --SPOILER-- All the mystical black magic stuff is a hoax, just trickery. I liked that - you get the creepy atmosphere, but reason triumphs.