For the first 58 pages of this book, I had a difficult time staying awake. It was the lists that got me. And the comma splices, which made even independent clauses seem list-y. 
 As other reviewers have mentioned, especially during those "creation-of-the-world" sections early on, the lists could easily run the length of a page. And if you're not familiar with a comma splice, it's the term that was written multiple times in red on nearly every undergraduate English paper I turned in. I got my B.A. in English; comma splices were the bane of my existence. I can recognize them now and they haunt me in other people's writing, a legacy passed to me by my professors. 
 In Byatt's Ragnarok, the shift came when the giant snake Jormundgandr arrived on the scene. The lists seemed to be shorter and come less frequently. The comma splices continued but commas were occasionally exchanged for semi-colons or, oddly, colons, which offered some variety. But mostly, the descriptions of Jormundgandr really caught my imagination. Finally, I could see what the thin child saw in the old Norse myths. I no longer struggled to stay awake. 
 Ragnarok the myth is both vivid and bleak. It's not a story of hope. It's a story of beings acting out a chain of events that has always been on the page. Even when one makes an effort to change fate, it's clear that it is just that: fate. It ends in The End. It cannot be changed. 
 There's the bleak. 
 The vivid is in the descriptions of the gods and monsters, both their appearance and their emotions: these are big creatures both physically and emotionally. Of Jormungandr, Byatt writes: 
 "The flung snake fell through the firmament in shifting shapes. With her spine locked she was a javelin, swift and smooth, her mane of flesh-fronds streaming back from her sharp skull, her fangs glinting...She was a sensuous beast: the rush of air pleased her: she snuffed up the scent of pine forests, heathland, hot desert, the salt of the sea." 
 It's description like this that I read and say, "Ah! There's the language people rave about when they talk about Byatt's work!" I have a clear image of what Jormungandr looks like (even if I can't pronounce her name), and thanks to the lush descriptions, I have the same for most of the other gods and monsters. The only tale with which I was familiar was the one about Baldur's death, and even that Byatt told in such a way that I saw the scene and the intricacies of the characters more clearly than I had reading other versions of the story. 
 Byatt tells the myths alongside the story of "the thin child," a character who represents Byatt's own wartime childhood in the English countryside. The thin child is drawn to the old Norse stories in large part because they echo her life both in the vividness and the bleakness. The thin child is in the middle of this time of both great freedom (from her asthma which is better out of the pollution of London, from the social roles of peacetime, the "dailiness," as she calls it) and great fear (of the possibility that her father won't return, of the "enemy" whose bombs rumble even this far outside the city). She deals with this by expecting that her father, off fighting the war, will not return. She accepts this, as the gods in the myth accept that the end of the world is inevitable. I think she finds a kinship and a comfort in this hopelessness. 
 "Imagining the end of things, when you are a child, is perhaps impossible. The thin child, despite the was that was raging, was more afraid of eternal boredom, of doing nothing that really mattered, of day after day going nowhere, than she was of death or the end of things." 
 And then the myth ends and the war ends and, it seems to me, the thin child is left to herself. Perhaps it's her age and would have happened anyway, but Byatt links this feeling of malaise and confusion with the end of the war and her family's return to their London home, and Ragnarok and the end of the world and the end of the myth. The world didn't end, and that seems to inspire a feeling akin to disappointment in the thin child. 
 "This is how myths work. They are things, creatures, stories, inhabiting the mind. They cannot be explained and do not explain; they are neither creeds nor allegories. The black thing was now in the thin child's head and was part of the way she took in every new thing she encountered." 
 The "black thing" to which Byatt refers here is the image at the end of the myth and the end of everything, but the "black thing" is also the fear and the feeling of inevitability that her father will not return. She carries the black of both with her even past her need for them, and every future experience is shadowed by it. 
 So, as you can see, while I felt the book had a slow start, I stayed awake long enough and it caught me eventually. I'm not going to go all gaga over A.S. Byatt, but I can certainly see what all the fuss is about.