We saw the Sherlock Holmes film this past weekend. I went in with very low expectations. I assumed there would not be any kind of a mystery, and that the characters had been vaguely inspired by the books, but more or less completely re-envisioned. I also thought Robert Downey Jr. was too nice and sweet to be a good Holmes.
I was surprised to find that not only was there an element of mystery, but its resolution was based on Holmes' keen obseravtions and vast knowledge, which is very much in keeping with the books. And likewise for Downey/Richie's interpretation of Holmes. The detective is not the same character from the books, but he is very much in the spirit of the "real" Sherlock Holmes.
And that's probably the most one can reasonably expect. I suppose Sherlock Holmes as written by Conan Doyle and illustrated by Sidney Paget is too vivid a character ever to be depicted accurately on screen. A good movie adaptation shouldn't aim for slavish imitation, and I thought the film did a good job of creatively re-imagining Holmes while also remaining faithful to the essence of the character.
The portrayals of Watson and Irene Adler were much freer, which is understandable. They weren't all that interesting to begin with so it's not distressing to see them conformed to fit contemporary character types.
I think that of the four of us who went, as the only Sherlock Holmes / Arthur Conan Doyle fan, I enjoyed the film more than anyone else. (Other people's comments were along the lines of "Not bad at all!" and "I would watch a sequel"--I was like "Woohoo! That was fun! That was about as good a contemporary re-imagining of Sherlock Holmes as one could hope for!") So, if you've been trying to decide whether to see it or not ... there's my estimation, for what it's worth.