You can read the wikipedia page about the movie here.
9/10. I cried when I watched this movie. This movie is sooooo well-crafted, thoughtful and delighted, while also being lack of Sherlock Holmes’ thrill. There’s a lot of things that will bring the memories of the case being solved by our beloved private investigator, for some he said being exaggerated by Dr. Watson. The saddest part of this movie was to know that the world most well-known detective was suffered from Alzheimer in his old and lonely days, out of this world as part of his punishment to himself for failing to solve his last case.
McKellen is dramatically brilliant, while other casts like Laura Linney and Milo Parker were also out of his shadow and stand their own characters.