NB: I have only watched Series 2, but I don't think I should be obliged to watch everything, which I don't intend doing, before posting a bad review.

The idea of updating the Holmes stories to the 21st century is clever, but it is only worth doing if you get more from the update than you lose. Updating the techology is easy, but there is so much more to the original Holmes stories than gas lamps and hansom cabs. The original Holmes stories were deeply embedded in the intellectual environment of the 19th century, referring to Carlyle or Wynwoode Reade or Jean-Paul or Wagner (to mention just a few examples) far more than other detective stories of the time. Although in the very first pages Conan Doyle seems to have made Holmes a thinking machine like the machine played by Cumberbatch, he rapidly changed this into a much broader, sometimes fallible and human character. Cumberbatch's Sherlock is a pure thinking machine, as if Google were to program a detective bot.

It's typical of this that, at least in Series 2, Cumberbatch's Holmes is unable to act his way out of a paper bag. The original Scandal in Bohemia includes two scenes where Holmes is able to convincingly portray other characters, in a "Scandal in Belgravia", Sherlock attempts one impersonation and is made in five seconds. Sherlock lacks the ability to empathise with others and so cannot act, unlike the original.

In fact, the 19th century fictional detective "Sherlock" most reminds me of is not Holmes, it is Austin Freeman's Dr Thorndyke, who featured in a series of (rather boring) detective stories high on analytical reasoning but lacking all of the other features which made Conan Doyle's stories interesting.

On top of that, the plots are ludicrous. In "The Reichenbach Falls" Sherlock assumes on very little evidence the existence of a simple computer code sufficient to break into all computer security systems. This is pure hokum, worthy of the best 1950s B Movies. (Remember the one about the atomic radiation which caused house-flies to grow as big as elephants? That kind of thing.) Steve Moffat can get away with this kind of thing when he writes episodes for Dr Who, Whovians don't have a problem with Atlantis being destroyed several times over in different ways, or London being invaded by aliens for no particular reason several times a year. But Conan Doyle tried to make his plots, if not plausible, at least appear plausible. The original Holmes was no superman, but based on a lecturer Conan Doyle knew at medical school.

My favorite Holmes: Clive Merrison in the BBC radio series. Against him Cumberbatch is just a caricature.