As someone whom is way more than a Sherlock Holmes aficionado (I have read all 4 novels and all 56 short stories by Doyle), all I can say is Downey was exceptional; Ritchie’s directing was spot on; and Jude Law makes a superb Watson.
That said, the true question is does it compare to BBC’s modernized Sherlock? In my opinion, they’re incomparable. The tv series provides room for characters to evolve, and they do. Plus, it takes place in modern London. Although his portrayal is so uniquely peculiar, I’d say Cumberbatch’s performance is as good and maybe even slightly better than Downey’s, but one must take into account that Downey had to craft a British accent which was a natural dialect for Cumberbatch. The BBC Ms. Hudson was perfectly cast and well-played, another dimensional development to the TV series. But I believe I prefer Jude Law as Watson to Martin Freeman. Loved them both. Kudos to Ritchie.
Conclusively, as a movie, the Ritchie direction was incredible and Downey’s action Sherlock Holmes is riveting.