King Arthur and His Knights of the Round Table is a detailed, authoritative _and_ exciting account of the Arthurian epic from beginning to end. Roger Lancelyn Green brought all his scholarship to bear in getting the details just right from the source texts, and, as much as possible, preserving even the original phraseology, including the memorable "'Where,' he said 'is the governor of this gang?'" in Sir Gawain and the Green Knight.
This is not simply a translation, though. Unlike the Greek and Norse myths which were consciously reworked over many hundreds of years into a form of coherence, the Arthurian cycle is complex, diverse, and frequently self-contradictory. Many of the writers themselves misunderstood their source material.
In his introduction, Green explains why and how he wove this tangled thread of tales into a single epic. The result is a masterpiece of its kind. This is not a book of fine descriptions, insightful character development or lyrical speeches. It is written in the epic style with the epic voice, and, in so doing, tells a story whose power is chiefly in the episodes and the figures, rather than in the realisation and the characters.
Roger Lancelyn Green introduced me to the Greek, Egyptian and Norse myths, and I owe him a lot. They opened a door to the original texts, which later came to play an important part in my education. But as I grew up I discovered that the original texts were better than the Green retellings. This, of course, is to be expected.
With Arthur, though, I have to say that Green's book really does work for me better than Mallory or Chretien de Troyes. In rereading it recently I realised why so much of Arthurian lore seemed second nature to me while studying middle-english at university - I had read it all before in this book.
I would recommend it to any child with an enquiring mind - it opened the Matter of Britain to me, and it will do so for them.