I finally read the Stealer of Souls and Stormbringer (originally published 1961-1964) - using the 2008 Del Ray edition. It looks like it has the original magazine versions.
Moorcock mentions in a 1963 essay later that he cleaned some of it up for when it appeared in the early editions of the books. and says "I'm not heavy with any of the magazine stories as they stand and have made, in places, quite heavy revision." It makes me wish I had purchased a different edition with that editing in it. The writing itself in the early stories was not good. Not surprisingly though, for someone in there very early 20s, it got better quickly, although it still isn't always solid.
If Law and Chaos has one wondering if Anderson's "Three Hearts and Three Lions" was a big influence, Chapter 3 of Doom Lord's Passing seals it I think. He credits both 3H&3L and Zoroastrianism for the Elric cosmology. In regards to Anderson, as of 1963 he thought "The Broken Sword" was the high point and the later stuff wasn't as good. In regards to Moonglum, Moorcock mentions being a big fan of the mouser.
Moorcock's introduction at the beginning and his acknowledgements at the end give me a different (more positive) impression of him than some of the earlier snippets I've read of his. Alan Moore's foreword was bizarre (but not unexpected).
I'm not sure, based on these two if I'd call it Sword and Sorcery. Maybe I'd have to read the other volumes to get that? And I'm not sure I'm interested enough based on what's here. Anyone have a recommendation for jumping in for more to get that flavor of it? I might follow Moorcock's suggestions and get The Broken Sword or check out Mervyn Peake's works for the time being.
Just a quick note looking at that list: Nine Princes in Amber and The Guns of Avalon are only two books in a 5-book cycle, which is itself the first half of a 10-book series. There's almost no resolution in just reading the first two books; read the whole Corwin Cycle. Compared to modern books it's not a particularly long read - if published now all 5 would probably be a single book.
Also, as you may have guessed from previous comments, I agree with Moorcock. The Broken Sword is better.