I think Stephenson did explain Enoch's presence, somewhere in his festival of words, but damned if I can remember what it was. With Stephenson I think it's just best to let the plot wash over you and not think too hard about it. But yeah, I wish he'd reel it in at times.
I liked Graham Greene's
The End of the Affair. Lots of wizardly turns of emotion and phrase. Praise to the author's craftsmanship.
And I finished Brandon Sanderson's new Stormlight book,
Oathbringer. The plot is getting a little contrived, and it's tough to keep up with a handful of new characters he focuses on -- is this person a Radiant or a Herald or a Voidbringer? what exactly are their special abilities? what's their Shardblade's name? -- but the overall story is interesting and the main characters continue to shine. For a series where each book is almost as long as the entire Lord of the Rings trilogy, it's impressive how the pace seldom slackens and the main characters remain intriguing throughout.