I can't say that I've ever actually read the Sherlock Holmes books. I do remember seeing the old black and white films though. I found them to be somewhat flat and rather Clue-ish... but done in all seriousness, which rather robbed them of impact or suspense. So it's safe to say that my first experience with the Holmes mythos starts with the Guy Ritchie film.
With regards to plot intrigues, this film is rather thin on them. A sharp observer can get the gist of it within the first fifteen minutes or so. In addition, I felt that the whole supernatural aspect of the plot device rather silly and slightly dull.
However, as I continued watching the film, it became more and more clear that the case that Holmes and Watson were attempting to solve was more a side note to the real plot of the movie: Holmes dealing with Watson getting engaged and moving out. Indeed, the character byplay between them made me forget entirely that this movie was "supposed" to be about solving a case, it was that much fun. For that matter, the sound editing fully backs it up as a character story. There are points where the sound becomes as one character would hear it, lending an almost first person feel to some of the scenes, even though they were not shot that way.
Anyway, I thought that the acting was excellent and splendidly entertaining. I could not get enough of Watson and Holmes sniping at each other. Fans of the older Holmes movies might disagree with Watson's portrayal, as Jude law is neither short or rotund, but I found that it worked for this movie extremely well and made it more of an equal partnership between the two men. The little hyper-analytical segments before Holmes smacks someone around managed to speak volumes about him in a very small space of time and his pervasive social ineptness made him into a more believable character. The female characters weren't all that bad either, with Mary providing a quiet foil to Irene's outspokenness, but both having a great deal of capability in totally different arenas.
All in all, I found this to be less of a detective mystery type story and much more of an action adventure with awesome characters. Again, I have no idea how close to the books this film is, but rest assured, I will be finding out. In any case, I will probably continue to enjoy the movie regardless.