The following is spoiler free - As a huge Holmes fan, I have to say that was one rollicking, awesome experience. Seriously, go see this movie. See it twice, because I want Ritchie to make half a dozen sequels.
The issue some people seem to have with Holmes being in an 'action film' as it has derisively been called by some is unfounded and rubbish. Yes, there is quite a lot of action to be had, but it is not at the expense of the character himself. What this movie did was take a side of Holmes from the stories - the side that could send a man away on a cart while he himself but sustained a black eye - and magnified it, put him in a situation in which he would have to use such physical adeptness in order to survive. And not only that, but through the action, we were able to glimpse the minute workings of his mind as he planned out his moves, like a chess-master. Seeing it in slow-mo and then in realtime was especially effective, I thought.
Downey is absolutely awesome at playing quick-witted one moment and scruffy and befuddled the next, convincingly going from hyper-observant to crawling about awkwardly in the sunlight after having been cooped up for 3 months without a case.
Watson was straight from the books. Unlike what the Rathbone pictures and other media popularized, Watson wasn't a baffoonish idiot. He was Holmes' best friend, a man he could depend on to pick up a revolver and give chase through back alleys in a pinch. Sometimes I thought Watson seemed a tad TOO sharp, but as someone who saw the movie with me pointed out, by acting slow at times Holmes was but leading his friend on, teaching him, encouraging him to use his own powers of observation. These sort of dynamics and the general banter between Jude Law and Robert Downey Jr. - who have excellent chemisry together, by the way - are what really propel the film, and it is this heart of the movie that makes the action worthwhile, not the other way around.
I was also highly appreciative of the point in time in which they chose to show the relationship between Holmes and Watson. It is a time far after they met and have already been on a great many adventures, when Watson wants to move on with his marriage but, as Holmes tells him in the movie, he doesn't quite want to let go of the macabre. He will still pick up the gun that his colleague deliberately leaves behind, just as Holmes knows he will. I do not know if I have seen a better Watson.
I liked little things like the mention of Mycroft Holmes. It surprised me when Holmes said 'The game is afoot'. I thought they would avoid that quote, originally from The Adventure of the Abbey Grange and later popularized by subsequent adaptations; however, at least that was from an actual story. Thankfully, they avoided 'elementary, dear Watson', which never actually appeared in a story (though there was a similar quote). I liked when Watson got on Holmes while in jail about how much Holmes withholds, something which has long been lobbed at the Holmes stories as a major criticism. I also enjoyed all the references to Watson's notes he took on the cases, something which is often glossed over in adaptations. That was how the stories were to have come to light. And interestingly, in the original stories, Holmes often chided Watson on the fantasic manner in which he presented some of the cases, something which lends some credence to the liberties taken in the movie, as they were always supposed to be presented in a popular fashion.
One of the principal liberties they took of course involved the character of Irene Adler, who appeared in but a single story. It was never a sexual thing between them, at least not on the surface. Holmes was primarily concerned with the fact that she was an intellectual equal, having outsmarted him in the story in which she appeared. That said, I didn't think her part detracted anything from the fun to be had in the film.
The music was fantastic. Hans Zimmer did an excellent enough job that I intend to purchase the soundtrack in the near future. The overall mood of the film was very nice. London has never been grungier.
Some parts WERE a little James Bond-ish, such as the big-man-versus-little-man fights and the climax, but this movie kicks the panties off of any Bond movie I've ever seen (though I haven't seen the Daniel Craig outings). So yeah, this ain't your grandpappy's Holmes, but it doesn't need to be. All 56 short stories and 4 novels are still there to read (and I've read 'em quite a few times by now). This is just another look (and a fresh one) at the Holmes character, one which I must say I thoroughly enjoyed.
I really, really hope this movie does well. One could do worse than have a few more outings with Downey and Law on the trail.