This movie review is provided courtesy of Cress. Thank you, Cress!
Now that I've seen the movie a second time, I can write a proper review, instead of just squeeing like a fangirl. The film certainly has some flaws and plot holes, but it remains an enjoyable ride. It is indeed an action-adventure flick more than a mystery, so you shall have to endure some slow motion shots, grandiose explosions, and gratuitous violence. (But I have seen other Holmes movies with self-indulgent, unrealistic fights, such as The Seven-Per-Cent Solution, which featured an absurd sword duel inside and on top of a train car, even though both opponents had guns!) There are also supernatural elements to the plot, but only in the same sense that HOUN relied upon a supernatural legend.
You also must accept that Downey's Holmes is going to look perpetually scruffy; this does go against canon descriptions of Holmes's catlike cleanliness, but it also makes sense in context; given Holmes's frequent need to disguise himself as various disreputable characters, he would need to have a five o'clock shadow and be ill dressed. After a while you get used to Holmes's appearance, and get to enjoy the elegance of Jude Law's Watson instead. (Although I personally hated the black uniform that Watson wears at dinner with Holmes and his fiancee.)
Speaking of Mary Morstan, the movie takes liberties with her background. As we know, in the canon, she was Holmes's client in SIGN, and both her parents were dead. In the movie, Mary Morstan has never met Holmes before, yet Watson is engaged to her. He also is supposed to go to tea to meet her parents. Before you scream about the "wrongness" of this chronology, please remember that Doyle himself made this mistake. In FIVE, Watson is married in 1887, but his wife has gone to visit her mother; there is a later reference to SIGN within FIVE, making it clear that the wife is Mary, not some unknown earlier wife. So imagine the movie as an alternate universe if you will, and go with the flow.
Irene Adler's history is altered too; she apparently has met and defeated Holmes twice before, and she is currently "between husbands." However, the most worrisome scene shown in the movie trailer--that of Irene Adler in a red corset attacking Holmes--is not in the final film at all, so we are spared seeing her look slutty. She dresses modestly most of the time and also wears male clothing. It appears that she likes Holmes more than he likes her. He seems fascinated by her criminal behavior and her ability to outwit him, but it is she who tries to kiss him romantically. That was one of the pleasant surprises in the movie.
The slashy content is very high; it is indeed a full blown bromance. You can see it from the first moment that Holmes and Watson greet each other. Even while they subdue an attacker, Holmes wonders if he left the stove on at home, and Watson tells him that he did, before complimenting Holmes's new hat. They behave very much like an old married couple, sometimes arguing and sometimes laughing together. They have a pleasing tendency to touch each other, and they are equal partners in their work; Holmes may be smarter, but Watson is a capable doctor and even participates in Holmes's deductions from a watch.
Indeed, I think that the whole movie is Guy Ritchie's giant love letter to the Watson of the canon. It reads, "I'm so terribly sorry that too often you have been portrayed as stupid, old, and fat. Here, why don't you enjoy being smart, young, thin, and HOT for once? Plus here's a spine with which you can yell at Holmes and even punch him for being a jerk. You get your dog, and your gambling habit, and Holmes mooning over your engagement. You'll survive terrible explosions, recover surprisingly quickly, and kick ass all over London. Love and kisses, Guy."
That said, there were still parts of the movie that bothered me. There's the unexplained beginning where Holmes runs through the streets like a fugitive. I don't understand why Holmes couldn't come in the same cab with Lestrade and Watson. I also didn't like Holmes's strange behavior to Mrs. Hudson, calling her "Nanny" and accusing her of poisoning him. I much prefer Holmes not to be hostile to her, or at least for Mrs. Hudson to have a sarcastic reply. As I mentioned before, I absolutely hated Watson's black uniform, and I didn't like that they couldn't outright say that Holmes took cocaine, let alone injected it. But overall, I don't regret seeing the film for an instant.