The Worm Ourorbos was originally published in a very limited and now very rare edition in 1922. Eddison wrote three sequels set in roughly the same universe, but none of them have the sustained pacing and invention of Ouroboros.
Before diving in, there are a few things to be aware of. The rich language Eddison uses is based on Tudor and Jacobean English, with some modern anachronisms; it may take some getting used to, and occasionally a trip to the unabridged Oxford English Dictionary. The narrator, one Lessingham, who appears in a very brief framing sequence, disappears a few dozen pages in. The book is set on Mercury; however, keep in mind this is not science fiction, so this is not literally the planet Mercury. Eddison on several occasions in the body of the book calls the world 'Middle Earth', and the setting is recognizably the Midgard of the Norse myths and sagas, although for some unexplained reason the denizens worship the Greek pantheon. The cast of characters, like Tolkien, are principally masculine, albeit with a couple of standout female leads. And lastly the various nationalities (Demons, Witches, Pixies, Imps, etc.) are not really separate species as in Tolkien; they are all essentially humans.
Once you get past these details, The Worm Ouroboros is a thoroughly enjoyable book which will satisfy anyone who has finished the Lord of the Rings and wants a new immersive universe.
This Kindle edition includes a map not available in the original, for which I am solely responsible.--J.B. Hare