Should this be Sherlock's final problem?

I've been a huge fan of the BBC series Sherlock since the start and was pleasantly surprised when the episodes of series four premiered on Netflix merely a day after they were aired in the UK. (A bit tough on those who don't have Netflix, but there you go.) At the same time, I was a bit apprehensive. The Christmas special The Abominable Bride from approximately a year ago wasn't much to write home about in my view - it over-used the dream-within-a-dream conceit to a ridiculous extent and was at the same time faintly preachy about Victorians and their views on women. So had Sherlock ended up being just a little bit too much in love with itself?

Well, hard to say. Series four was better that The Abominable Bride, but a certain smugness does seem to have crept into the franchise. Of course, in a way, it was always there. The previous episodes have had plenty of tricksiness-for-its-own-sake scenes, and sometimes when Sherlock was behaving badly and getting away with it, you felt that there was an element of wish-fulfilment about it on the part of the script-writers. But you were prepared to overlook it and embrace the clever-clever style, because at the heart of the story was the touching friendship between Sherlock and Watson which made the show into something more than a series of mind games. The side characters were engaging, too, and the acting was always top notch.

The side characters are still good (though Lestrade and Molly get a little short-changed this time around) and the acting's still marvellous. But the main problem for me with series four is that suddenly I stopped caring about the Sherlock-Watson friendship. I thought the series makers dealt well with the potential hurdle of Watson's marriage in series three by making his wife, Mary, an extraordinarily clever and unpredictable woman who unexpectedly really liked Sherlock. It appeared the transformation from dynamic duo to dynamic trio had been successfully negotiated: however, in series four, the strain starts to show. The focus changes from Sherlock's and Watson's relationship to each other to their relationship to Mary, and when they find themselves down to two again, some of the old warmth has been lost along the way.

Because this vital part of the setup didn't work, the show's weaknesses appeared more clearly. Sherlock's flippiness and Watson's staidness started to grate in a way they hadn't done before. Then there was the smugness. The Six Thatchers wasn't quite the anti-Thatcherite tract which some reviewers claimed - as in the story it was inspired by, The Six Napoleons, six busts of the titular statesman/woman are smashed to pieces, but the identity of the smashee doesn't prove to be important - but still there was a sneering undercurrent in Sherlock's comments about the first bust-owner's collection of Thatcher memorabilia which ill accorded with his character. One must remember that Sherlock, though played by Benedict Cumberbatch, is not in fact Benedict Cumberbatch, but a detective obsessed with solving puzzles and with little time to spare for having fashionable opinions about current affairs. This wrong note was made worse by the fact that the said bust-owner, a Tory MP, had just lost his son in a heartbreaking mini-mystery-within-a-mystery incident which was easily the most affecting part of the episode. Sherlock was rude to the grieving parents, as could have been expected, and more intent on the minor but intriguing problem of the missing bust than on explaining their son's death, which I can also buy. But preening luvviedom on top of that? Please.

Nor was this the last time Sherlock got my goat in this episode. At the end of it, he made a belittling speech about the main culprit's supposedly humdrum life, a speech which proves to have dire consequences - but the life in question didn't sound so bad to me. In fact, it sounded a bit like my life. What kind of rarefied air do these people breathe if they think a perfectly decent nine-to-five job (and in London, for heaven's sake) must needs make someone embittered and jealous? I don't begrudge anyone the thrill of working on a labour of love as Sherlock and getting paid for it too, but they needn't be patronising prats about it.

The following two episodes dialled down the smugness, and episode two - The Lying Detective - was probably the best in my view, not least because of a stellar performance from Toby Jones as Culverton Smith, a rich and respected businessman and philanthropist who also happens to be a serial killer. Here's the thing, though: at least the nine-to-five villain was sane. In both episode two and three, Sherlock once again goes with the "barmy villain" plot.

I've accepted that Sherlock baddies will usually not float my boat - neither Jim Moriarty nor Charles Augustus Magnussen was designed to make even my villain-loving heart flutter - but two psychotic villains in a row does seem like a cop-out. After having been pampered with the careful villain-character-building of Once Upon A Time, it was especially hard for me to accept as the only rationale of an antagonist's behaviour that he/she was loopy. Then again, Once is more villain-orientated than Sherlock (in fact more villain-orientated than most shows, bless it). In Sherlock, the villain's main function is to prove an intellectual challenge worthy of the ultra-smart detective: psychological credibility is optional. When you're starting to become a little disenchanted with said detective, though, the crackpot-genius enemy storyline doesn't feel strong enough to fully engage you. The plot of episode three, The Final Problem, reminded me of an Avengers episode going extra dark (that is, The Avengers as in John Steed plus feisty female sidekick, not as in superheroes). Nothing wrong with that, but you expect a bit more emotional heft from Sherlock.

The Final Problem needn't, in fact, be the final problem of Sherlock. Do I think it should be? Well, not really: I still enjoy the show too much not to want to watch more of it. I liked seeing so much of Mycroft, and the running joke in episode three about him once having played Lady Bracknell in a school production of The Importance of Being Earnest was both sweet and funny. (The series could in fact have benefited from more fun and sweetness in the same vein.) If Sherlock series five comes along, I'll not be complaining. But they need to watch their step.