There has been a rash of Sherlock Holmes adaptations in the recent past - from the action hero, to the modern adaptation to the faithful reproductions. In this crowded space, Mr Holmes is different - an aged, retired Sherlock Holmes tries to reconstruct his final case that led him to retirement - but his failing memory and body doesn't help his cause. In between the case recollection, there is a small side story about a Japanese man helping him with "medicinal" assistance to improving his memory and a great story about his widowed housekeeper and her young son; and more importantly the relationship between Sherlock Holmes and the son.
The highlight is undoubtedly the acting - of both Sir Ian McKellen as Sherlock Holmes and of Milo Parker as the inquisitive young boy. The performance of Ian McKellen as a 90 odd year man, losing his memory and for that matter other physical abilities was just astounding - especially given his rather superhero performances in the X-Men series and Lord of the Rings. The plot is rather mundane, there is not much in the mystery to be honest (and it somewhat goes against Conan Doyle's characterisation) - but the acting is a joy to watch.