A comic book has been longlisted for Man Booker prize.

The Man Booker Prize for Fiction is a literary prize awarded each year for the best original novel written in the English language and published in the UK. It is prestigious and influential.
The book is 'Sabrina' by Nick Drnaso.

A comic book being included among the contenders for the prize means literary people regard this book as a literary work and are passing judgment on it as such.
Many toilers in the field of sequential pictorial narrative will be chuffed to have their chosen livelihood acknowledged as worthy by the keepers of our literary heritage. Paul Gravett was pleased.
Me not so much.
My first, and ungracious,response is more "Keep your manicured hands and manicured minds off our stuff."

It is a category error. It confuses literature with story-telling. It takes the marketing phrase 'graphic novel' at face value. Tarzan books and Tarzan comics are not the same experience. Each art form require a separate, different and particular set of values in order to evaluate them.It is apples and oranges.

Comics are great but I don't believe they have yet produced a Dostoevsky, Thomas Mann, Virginia Woolf, Joseph Conrad, or a George Elliot.
Novels are great but did not produce Superman, Silver Surfer, Dan Dare, Krazy Kat, Popeye or . . . make your own list.

More and different at -
https://www.drawnandquarterly.com/sabrina
https://www.theguardian.com/commentisfree/2018/jul/25/man-booker-literat...
http://theconversation.com/graphic-novels-are-novels-why-the-booker-priz...
https://www.ft.com/content/97bd2cc0-966f-11e8-95f8-8640db9060a7 - where the 'not thrilled' view is shared.
and this to show something about the uniqueness of comics - https://www.cbr.com/she-hulk-fantastic-four-homage/