_Pendragon_ seems older than its publication date of 1930. It has digressions from the plot which are lengthy (but not to say uninteresting), and it uses a lot of old-fashioned words (e.g. leman, agnate, kern). It is also jarring to modern sensitivities the way the British enemies are treated e.g. Arthur says "To my mind the battle is not over until ... all the prisoners [have been] flogged and slain." Nevertheless Faraday somehow manages to keep a light touch, so the novel is surprisingly easy to read.
It tells the story of just one year in the history of Britain, 502/3, but what an year! Faraday packs his story with characters and events from throughout dark age history. e.g. it features Drust, king of the Picts (usually dated in the first half of the 5th century) and Urien of Reged (usually dated in the late 6th). And it includes both the Night of the Long Knives and the battle of Badon. It is also a love story (though a very chaste one).
When it comes to historical accuracy, _Pendragon_ suffers from having been written when much less was known of post-Roman Britain. Faraday's Britain of 502 A.D. is much more like the Britain of 3 centuries earlier (apart from the spread of Christianity). It still has "Great and beautiful cities". It still has 3 legions to defend it, each with 5000 men equipped with square curved shield and short swords. The size of the enemy forces (half a million Picts, Scots and Saxons) is ludicrous. But if you read this as an historical novel in both senses of the word, then maybe you can regard these anachronisms and exaggerations as part of the book's charm.