The script is one of the weakest parts of this movie. While I don't mean to suggest that it is a bad script, it does fall into two of the traps that historical action-y movies generally succumb to. First, and somewhat surprising, is the comically strong female character. Now, before you get angry and start calling me sexist, read the next four sentences. I loved the character of Irene Adler in Doyle's story "A Scandal in Bohemia." In that story, she beats Holmes at his own game. What I object to is the modern trend of assuming that any woman who is going to be a strong character in an action-y movie must either be a thief or an assassin or something, and must be able to kick as much ass as any man can. This is the problem with the film's version of Adler. I think that the most compelling thing about the character of Irene Adler was her ability to match Holmes on a mental level. Doyle's version of the character was never a badass tough guy, but she was much more interesting.
The other problem the script had was the one that everyone knew it would have. Unnecessary and unexplainable anachronism. There was enough interesting and bizarre technology in the late-middle nineteenth century that we don't need to have the characters invent tazers. I realize that this is a pointless request, but hey, Hollywood, if you're listening, STOP IT! There is no need to pull this crap, and it never adds anything to the movie. I am always reminded of the nadir (it's a real word, look it up) of the historical action-y movie genre "The League of Extraordinary Goddamn What a Terrible Movie," when captain Nemo reveals his eight wheeled "Auto-Mobile."
Side note: Sorry that the last two paragraphs resemble a loosely organized rant about what is lazy and stupid in the movies, but the truth is that they were a loosely organized rant about what is lazy and stupid in the movies.
Back to the script. Other than the odd direction that the script took with Irene Adler and the stupid f--I promised I would stop rant--ing anachronisms, the script is strong. The mystery was well constructed and, despite my fears, actually something of a mystery. ish. The characters were well constructed and generally at least solidly two dimensional. Holmes, Watson, and the aforementioned Adler were fairly complex. Oddly enough, the writers abandoned Holmes' weakness for cocaine, legal at the time, for other ill-defined but presumably more "family-friendly" drugs. In my opinion, this doesn't reveal the weakness that Holmes tries so hard to conceal and overcome, so much as it makes him look like a victorian Hunter S. Thompson.
Which somehow brings me to the acting. Robert Downey Jr. is unsurprisingly great as Sherlock Holmes. He is at times (a phrase that seems only to pop up in reviews, I've noticed) hilarious and heartbreaking. The objective seemed to have been to humanize the man, and he could not have been better cast. Jude Law was marvelous as Watson, bringing a complexity and humor to the character I was most afraid would be sidelined. Watson is truly this film's heart (for the record, it caused me physical pain to type that). Rachael McAdams is good as Irene Adler, the love interest, but her character is too obviously Irene Adler, the love interest. A real standout for me was Mark Strong as Lord Blackwood, the villain. He brought a real air of menace to the character and occasionally threatened to steal the show.
Overall, I really enjoyed this movie, despite a few nagging details, but, and this is important, I am only a fan of Sherlock Holmes stories. I have no idea how a fanatic might feel about this movie. It is an unapologetically modern take on the character, which is most likely a smart choice in terms of box office revenue. Fortunately, the movie doesn't suffer for it. In many ways, it is reminiscent of this summer's Star Trek. There are one or two stumbles, but the movie should appeal to newcomers and, hopefully, die-hard fans of the original stories.