The biggest problem the movie has is the plot. It's ridiculous. Mainly it's and excuse to hang a lot of action scenes on, and there are plenty of those. I don't think you can find their equivalent in any of Doyle's stories, which are a good bit quieter and more contemplative. Not that they lack action. There's action in plenty of them. It's just not the kind of action that's in this movie. At least one of the scenes (in a smoke-filled room) was completely unnecessary. Holmes "learns" something that he already knew. We see a nice cat-and-mouse game and a cool escape, but the scene does nothing at all to further the story.
As for the characters, it seemed to me that the writers and director took things that were mentioned in passing in the stories and exaggerated them considerably (Holmes's boxing skills, his martial arts ability, his untidiness, etc.). I suppose this was necessary to ramp up the action, but it wasn't true to the spirit of the stories. That being said, I thought Robert Downey, Jr., was terrific as Holmes, as was Jude Law as Dr. Watson. Rachel McAdams was very pretty as Irene Adler. The CGI version of Victorian London looked great.
Guy Ritchie likes the kind of ending where things are summed up with flashbacks to the action, showing us things we might have noticed and explaining them. the technique worked pretty well in Sherlock Holmes context, I thought.
If there's a sequel, I'll probably be there. Judy probably won't.