I've just seen all of series 2 this week and it's brilliant!
I was prepared to hate the idea of Irene Adler as a dominaitrix (a real stereotype in crime shows these days) but they pulled it off by focussing more on her intelligence than her sexuality.
Hounds of Baskerville was a brilliant twist on the original and I loved Sherlock's big moment of self-doubt.
Reichenback Fall was the best of the series. I'm not entirely happy with Andrew Scott's version of Moriarity which (IMO) was a little close to John Simm's Master in Doctor Who. That's just a minor quibble, and the script was so smart, so tense, so funny and the ending so perfect, that it's not a problem.
It may not be fair, but I've been comparing this to the Robert Downey Jr. version and like it much better. There's a whole different feel I get from the two. With the Downey movies it feels to me like the writers have said, "Let's take this tired old Sherlock Holmes idea and try to make it cool."
With Sherlock, it's more like, "Sherlock Holmes is so cool and we love the original stories so much. How can we present this in a way that will let the audience love it the way we do."
I've written stories for a few licensed characters, some good and some awful. The awful ones are always for the characters i don't really like that much. When I love the characters, the whole process is different and I think that communicates to an audience.