I was a bit put off by Downey's muddled dialogue. Then I remembered it was about the same when he played Charlie Chaplin in the biopic of that (second) name back in 1992. Seems he didn't think much of practicing his accent through all those times in rehab.
I thought Mark Strong was particularly good. The friend with whom I saw "Holmes" briefed me on his CV a bit: a lot of period, Victorian romantic pieces. I found that explained what made the scene with the golden chalice in the Order's "temple" among the most memorable in the film. Good to see a man expand his range, also; no horse-blinders on Mr Strong when it comes to picking great projects (anymore).
Jude Law made an excellent Watson, imo. He buried (one hopes for good) the notion of playing him as a "dundering dull-head," all too common with the Rathbone-era (and subsequent) personifications of that character, and did so almost flawlessly. Good job, Jude!
All in all, a great effort carried off better than I expected. Well worth waiting to see what they do with the sequel(s).
BZT
(Can you tell YT has a mass-media degree, never properly applied?)