When I was at uni my creative writing teachers were very sniffy about genre fiction. "They're fine if you want to make money [who doesn't?] but they're not real writing," they'd declare. This stuffy attitude is lampooned in a popular cartoon, where a spaceman looks down at a huddle of literary types and retorts, "You're all just jealous of my jet pack!"

Though it pains me to say it, the older I get, the more I find myself moving away from genre fiction, both as a writer and reader. When you go on the Amazon Bestseller list in search of a new book, the same clichés pop up. YA dystopias, psychological thrillers, "women's fiction" ... If these particular subsets don't float your boat, you can despair. "I don't WANT to read Serial Killing By Numbers or Mrs Murgatroyd's Second Honeymoon!" you wail. You take to stalking the Guardian book pages or Recommended lists on Goodreads in the hope that elusive creature - the perfect book - will materialise.

Don't get me wrong, I don't hate genre fiction. As a kid I wolfed down fantasy: Harry Potter, Diana Wynne Jones's Chrestomanci series, Terry Pratchett's Discworld. (I was in love with Lord Vetinari and remain so to this day). I thought the transition to more adult fare would be effortless. Give me a feisty heroine on horseback or a mage wrestling with his dark side and I'd be happy.

What a letdown! Conventional fantasy was completely lacking in humour and vim. Chuck in a dragon, the rule seemed to be, and no one will notice the story's crap. You'd have hordes of hairy guys lifting utensils and crying, "I'm Groin, son of Loin!" If that wasn't bad enough, they'd sing in wholly made-up, untranslated languages for entire chapters. Gah! Every time a fantasy book arrives in the bestseller charts I hover, wondering if this will be the one to lift the hex. It hasn't happened yet.

The trouble with genre fiction is that for every Gone, Girl or The Hunger Games, you have hosts of imitations. (Can you tell all these "teen in a hellish world" sagas apart?) They saturate the market until the next craze comes along, perhaps reviving older (and better) works, but inducing inertia in readers. We've seen these exact same characters and situations before. There's nothing new or innovative here.

If this is unsatisfying for readers, spare a thought for the poor writer who's trying to do something different. There is only a limited number of descriptions available on Amazon; even if your book doesn't quite fit, you're forced to select one. Woe betide if your erotica doesn't involve CEOs tying up interns with gaffa tape or your romance doesn't have the stock archetypes readers apparently want. It's a recipe for one stars, simply because your book didn't meet a reader's expectations.

When I pick up a book and it goes against the grain, I'm delighted. The Time Traveler's Wife is an old favourite: it weds sci fi to romance, with the brilliant twist that time travel is a hereditary biological disability. I loved The Girl With All the Gifts, despite it being a genre I'd never normally touch. By the time you realise what's going on, the story's so good you can't put it down. Daphne du Maurier's The House on the Strand is possibly her weirdest book but one of her best. Thanks to a drug cooked up by a scientist friend, the narrator can go back to the fourteenth century - his mind in the past, his body in the present ...

The success of the first two books proves you don't have to blindly follow formulas to sell. Some authors make a living from being unpredictable chameleons: Margaret Atwood, Jeanette Winterson, Ian McEwan, Kazuo Ishiguro. You don't know what they'll turn their pen to next but it'll be a cracking read.