Brave man, Steven Moffat. First he takes on Doctor Who, with all that that entails in terms of a devoted fanbase and years of labyrinthine backstory. Then he tackles another iconic figure in the shape of everyone's favourite pipe-smoking, deerstalker hat-wearing, angular Victorian detective.

Working with fellow Who alumnus Mark Gatiss, Moffat's task was to make the modernised Sherlock stand out from the current vast crowd of police procedurals. Oh, and House, which has already taken the core of the Holmes myth right back to its origins in Arthur Conan Doyle's time at medical school.

As if all that isn't enough, there are the many interlocking segments of Holmesian lore to contend with, accumulated over years of successful previous adaptations. Basil Rathbone built on Sidney Paget's drawings of Holmes for the Strand magazine to create the iconic image in no less than fourteen films, while Jeremy Brett highlighted the manic streak in the detective's character in the popular ITV adaptation. Moffat and Gatiss had to update the world's only 'consulting detective' while somehow paying homage to all that had gone before.

Their efforts have certainly paid off. Sherlock is everything an adaptation should be, a fresh, exhilarating take on the great detective's story that manages to retain every bit of the original's atmosphere. No mean feat, considering that Moffat and Gatiss have lifted Holmes and Watson out of the smog-shrouded, gaslit Victoriana so heavily linked to Conan Doyle's work, and seamlessly grafted them onto the present day.

Oddly enough, though the ubiquitous hansom cabs have been replaced by taxis and the telegram by text message, nothing about the transition feels jarring. As in Doyle's original stories, Watson's just left the army after having been wounded while serving in Afghanistan, a conflict as resonant in nineteenth century England as, depressingly, it is today.  He also still serves as a chronicler of his friend's adventures, something that Sherlock, true to form, evidently finds both annoying and rather satisfying.

This Watson, however, has an online presence, and Holmes sarcastically asks how he could ever manage without "my blogger". Doyle's detective had asked the same of his 'Boswell', a reference to the close friend and biographer of the eighteenth century man of letters, Dr Johnson. It's a smart update, reminding us that, regardless of the medium, a fascination with gossip is one thing we definitely share with our ancestors.

Of course, any version of the Holmes myth stands or falls on its leading man. Does he fit our mental picture of the great detective? Luckily for this adaptation, Benedict Cumberbatch offers us a portrayal of Holmes that is pretty much definitive. Okay, so the accoutrements aren't what we've come to expect. Instead of the deerstalker and the cape, we get sharp tailoring and a rather fabulous coat, and why not?

We never actually find Holmes wearing his distinctive headgear until Rathbone donned the deerstalker cap for the films, which goes to show how much our impressions of a literary character are blurred by later representations that end up becoming part of the 'canon'.

Cumberbatch's Sherlock is wonderfully true to the spirit of Doyle's character. The angular, distinctive profile, the manic energy alternating with brooding listlessness, the killer sarcasm, the drug habit and, yes, that last one is no modern innovation.

If anything, Sherlock's addictions have been toned down for this version, although a strong hint was dropped when he let slip to Watson that a drugs bust in his flat was actually quite likely to turn up something incriminating. One of my favourite moments was when Sherlock revealed that a particularly taxing mystery was a "three-patch problem", pulling up his sleeve to reveal the sources of his nicotine fix. Swap 'three-patch' for 'three-pipe' and you're right back to Doyle's character.

As for his self-diagnosis as a "high-functioning sociopath", it would certainly explain a lot, though we've definitely had one or two glimpses of a heart hidden somewhere beneath that wonderfully acerbic exterior.

As for his companion, Martin Freeman's John Watson is an interesting take on the erstwhile doctor, choosing to highlight the steadfast, no-nonsense side of Sherlock's trusty sidekick rather than the permanently overawed buffoon we've sometimes seen in later adaptations. Here, Watson's a straight-talking military man who provides his socially inept friend with the moral compass and sensitivity gauge he so often needs.

Sherlock's narrow circle of acquaintances extends to his landlady, Mrs Hudson (a delightfully batty expansion of a minor role by Una Stubbs) who provides tea, sympathy and a distinctly skewed worldview as she soothingly tells our hero that what he really needs is to cheer him up is a "nice murder".

The watchful presence of his brother, the all-powerful civil servant Mycroft (played by Gatiss) is, again, pleasingly fleshed out, with the addition of a hilarious rivalry between the all too similar siblings.

Sherlock's occasional 'colleagues' at Scotland Yard are a mixed bunch. Inspector Lestrade (Rupert Graves) is, like Watson, closer to Doyle's creation: professional, tenacious and torn between antagonism and affection when it comes to Sherlock. The other policemen who help, or, more often, hinder Holmes in the original stories haven't yet made their appearance, although there are glimpses of them in some characters we have met.

The ambitious DI Dimmock could reflect Lestrade's bitter rival, Inspector Gregson, while the snidely resentful Inspector Donovan is more of a composite of every petty official Doyle forced Holmes to endure.

As for Moriarty, whom we briefly met in the dramatic cliffhanger to episode three, the change from a sinister professor to a dapper, youthful psychopath is certainly audacious, and seems to have divided opinion. It's going to be interesting to see how these changes play out in the promised second series.

The question is, where will they go from here? If this brief run is anything to go by, we can expect an exhilarating mixture of elements drawn from various Doyle stories and woven together with new twists. The magnificent opener, A Study In Pink, referenced more than the title of Doyle's first Holmes novel, A Study in Scarlet. The story of Holmes and Watson's first meeting through a friend at St Bart's was almost identical to Doyle's version, albeit with some lovely updated touches. Here, Holmes deduces Watson's life story from his mobile rather than his fob watch.

The serial murder case takes only the method (poisoned tablets offered to the victims as part of a Russian roulette-style gamble) from the original. However, Sherlock's inspection of the first crime scene contains one fantastic in-joke. In A Study in Scarlet, the word ‘Rache' is scrawled in blood upon a wall. Lestrade pompously insists that it's an attempt at the name ‘Rachel', but Holmes corrects him. It's actually the German for ‘revenge'.

Moffat and Gatiss wrongfoot us by switching the comments around, so that the message scratched into the floor by a dying woman is, after all, the name of the victim's daughter. This sets the tone for the series, The writers clearly love their source material, but far too much to be overly reverential.

The second episode, The Blind Banker, united plot elements from two Doyle stories, the novel The Sign Of The Four and The Adventure Of The Dancing Men, by blending a locked room mystery, sinister secret codes, and Watson's meeting with a future love interest.

Best of all, perhaps, was the finale. The Great Game adapted the plot of The Bruce-Partington Plans, in which the discovery of a murdered civil servant leads the discovery of a plot to sell sensitive details of a defence project, and wove it into a complex tale in which Moriarty, keen to become Sherlock's nemesis, set the detective challenge after challenge to solve against the clock with an innocent victim's life in the balance.

The countdown was announced with a sequence of ‘pips' sent through a mobile phone, a clear reference to the eponymous coded message of Doyle's story The Five Orange Pips.

Finally, in the cheekiest nod of all, Holmes came face to face with his enemy at a deserted swimming pool, an encounter culminating in a deadly impasse. With laser sights from several hidden snipers trained on him, Holmes pointed his gun at an explosive vest next to Moriarty, leaving us clueless as to whether he was preparing to sacrifice his own life to take down the kingpin of organised crime.

The concept of hero and villain locked in a struggle to the death was lifted straight from The Adventure Of The Final Problem, where Holmes apparently met his death as he and Moriarty tumbled over the edge of the Reichenbach Falls. It's still a cliffhanger, only without the, well, cliff.

Public opinion has won us a guarantee of a second series, just as Doyle was prevailed upon to miraculously bring his hero back from a watery grave over a century ago. Now all that remains is to wonder which elements Moffat and Gatiss will go on to pick out, and which they'll discard.

Will we see a crafty Irene Adler, the one woman ever to truly pique Sherlock's interest? Deadly snakes summoned by nefarious stepfathers? A really, really big, scary dog? It's all up for grabs. The game's afoot...