First, to get it out of the way: the worst, absolutely unforgivably worst, thing about the 1968 DAW edition of The Sword of the Dawn is its unforgivably bad cover. It's so bad I actually knocked half a point off the book's final rating. DAW, who usually came up with top-notch artists to do Moorcock covers, really dropped the ball in the Runestaff series, and this is the nadir. Cover it, school-textbook style, before reading.
That said, the book itself is top-notch, one of the better novels in the whole Eternal Champion cycle. Dorian Hawkmoon, reluctant servant of the Runestaff and another incarnation of the Eternal Champion, is off on the quest to find the last piece of the puzzle he needs to strike back at the Granbretanian army, an artifact called the Sword of the Dawn. Needless to say, getting his hands on it will not be easy...
The same cast of characters from the first two novels returns, along with some throwaway characters, a new villain or two, and all the adventure one could possibly want. As well, The Sword of the Dawn is set on a new continent in the purview of the Eternal Champion, Amarehk (yes, it is what you think it is), and Moorcock's descriptions of the city of Nawlin (yes, it's at the delta of the big river) are perhaps the most detailed urban descriptions in the whole series.
The novel could probably stand on its own without too much of the ongoing plot being lost, but aspiring Moorcock readers are encouraged to read the whole series (preferably after those of Elric, Corum, and Erekose, at least). ****