LC and I went to see this last night. It turned out to be very much not what I'd expected: I had expected this to be very much an "elderly Holmes takes on one last case", when in fact it turned out to be much more "old man deals with the problems of senility". In fact, it being Sherlock Holmes was largely incidental to the whole story
That said, it was a good film, albeit a fairly uncomfortable one to watch. Ian McKellan is great, which is hardly a surprise, and the cast around him do a very good job as well. And it was because the cast were so good that it was uncomfortable to watch - the whole thing just hit a little too close to home.
So, I'll recommend the film, but cautiously. And it may well be one to wait for on DVD/TV/whatever, as there isn't really anything to be gained from the big screen and high-end sound system of the cinema; it will work just as well from the comfort of the sofa.