Robert Macfarlane, Cambridge fellow, author, all-round good egg, is best known being one of the country's leading landscape writers.

His latest book, Landmarks, is the latest example, a lovely extended riff on literature and language. But when I went to speak to him at Emmanuel College last month he also reminded me that he is something of a graphic novel fan. He's even set the work of Chris Ware for his students.

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So it was something of a surprise then that he didn't know of the work of the Hernandez Brothers. Back in Scotland I sent him my review of Graphic Content's 2014 Book of the Year, The Love Bunglers. He emailed me back to say he had it on order.

Ever since, though, I've been worried that he won't get it. That Jaime Hernandez's book - despite the creamy smoothness of the art and the heartachey, heartbreaky, swell of the story - will be difficult for a new reader to come to terms with. A bit like starting to read a novel on page 150. The Love Bunglers is, after all, the culmination of 30 years of comic strips. A story that Jaime Hernandez has been adding to and adding to since the early eighties. Can you come to it fresh and truly take it in?

Still, there is one consolation. At least I didn't suggest he read the latest book by Jaime's brother Gilbert.

There's a caption on page 138 of Ofelia, the latest compilation of Gilbert Hernandez's ongoing Palomar strips, which informs us that the story that begins on the page features "Steve, Guadupe, Igor and more characters than you can keep track of!" How true, how true. Even though I've been reading his strips since the late eighties I still sometimes have to consult the family tree to work out how everyone is related.

While Jaime has concentrated on telling the story of his principal characters Maggie and Hopey, Beto's cast has grown bigger and bigger (in both numbers and bra sizes). And if his big-breasted heroine Luba is the star at the centre of this universe, there are many, many satellites circling her - her sister's Rosalba, aka Fritz, the psychotherapist with a lisp and Petra, the soccer mum and gym bunny. Then there's her cousin Ofelia, Pipo, the TV star, who lusts after Fritz; Doralis, Luba's daughter who also appears in Pipo's show and who may or may not be a lesbian and Sergio, Pipo's football star son and Fritz's lover. And that's only the bare bones of the cast list whose stories play out in America and in Palomar, Hernandez's imaginary Latin American playground.

Hernandez's stories amount to a dense spiralling narrative that jump back and forth in time and then strike off in unexpected directions. It's a Latino magic realist melodrama cum soap opera that accretes and accretes thrillingly with every new story. It's no wonder that in the inside back page of Los Bros Hernandez's mother comic Love and Rockets there's a note that says Hernandez's first book, Heartbreak Soup, is the "best place to start reading". It's easy to get lost in Palomar.

There's something else going on in Ofelia that should be noted too. It might look like a graphic novel but it's not. It's a collection of comic strips. These are different things. There's a danger that people coming to Hernandez's work may be looking for something more rounded, a story arc that is novelistic in structure; one with a beginning, middle and end. He can do that. Incredibly prolific, in recent years he has produced standalone graphic novels such as The Marble Season and Bumperhead which prove the fact. But that's not what is happening in Ofelia.

These are strips - originally created at the start of the century - which often have their own rhythm, their own tone, even though they are all set in the same fictional universe. They are short, sharp, flinty, dark, nasty, sometimes brutal and often lubricious strips that offer new layers to the bigger story but remain discrete in themselves.

And so right in the middle of a series of stories that graphically - very graphically - catalogue the sex lives of Luba and her sisters (prudish readers would probably be best to stay away) you can come across a sweet, funny eight-page strip that simply features Petra's daughter playing football. Dialogue, meanwhile, can veer from plain and functional to comic book baroque.

None of which is going to be welcoming to new readers. But for those who have put the pages in Ofelia is just the latest sample of perhaps one of the most ambitious achievements in comic book history. A huge sprawling story that combines the scope of a 19th-century novel with a post-Freudian candour. With his brother Jaime, Gilbert Hernandez has spent the last 30 years and more on one of the greatest comic book adventures. Even in partial form, it's a staggering achievement. He is a comic book Balzac.

Ofelia is published by Fantagraphics Books, priced £14.99.