It's weird, but in a good way. I should reread it.

As a reader of science fiction, all of the descriptions and reviews of this seem like yet another book that is essentially science fiction written by someone totally outside the genre.

That said, I LOVED Tenth of December.

But it is blurring the borders between lit fic and spec fic, from the lit fic side. Kind of the same blurry area that "Beloved," "Underground Railroad" and "The Buried Giant occupy.

It's certainly not science fiction that those of us in the s-f world would recognize. I've never read "Beloved". I have read "Undereground Railroad" and agree that it is in a blurry area.

One of the things that those of us in s-f are made crazy by, is that we are deemed less worthy than other forms of literature.

As someone once pointed out, "literary fiction" is a genre. Just like romance or mystery or science fiction. The only difference is that "literary fiction" is considered better than those others. Hah!

Lit fic has it's tropes just as sci-fi has it's tropes. And it doesn't sell as well! Of course neither sci-fi or lit fic sell near mysteries, let alone romance...
I like seeing literary authors play with sci-fi for several reasons, mainly because they don't know the rules they don't know they are breaking them. At the same time, I don't appreciate when they look down on sci-fi, like Margaret Atwood tends to. And Ishiguro made some statements that sounded pretty condescending about spec fic when he was promoting Buried Giant, but he later clarified that he was talking more about critical attitudes than the actual works.
But the best of spec fic can stand next to the best lit fic - no one can say that Ursula LeGuin was less of an author because she wrote about aliens and magicians.

Try 'The Years of Rice and Salt' for a really interesting read.

I remember looking, at the beginningof each section, looking at the initial letter of characters' names to re-orient myself.

He did one of the best jobs of alternate history I've ever read. And I love alternate history.

May I mention another:

Pastwatch: The Redemption of Christopher Columbus by, of all people, Orson Scott Card. Very interesting

Not alternate history, but two books that should be better known are Time on My Hands by Peter Delacorte and Replay by Ken Grimwood.

In the first a man who writes travel guidebooks is given a time machine on the understanding that he go back and prevent Reagan from becoming President. The man who originally has the time machine believes that Reagan was the worst President ever, and the country would be better off without him. The book came out in 1997. I read it then and have reread it several times since, but not since the current President took office.

The second asks the question, "What if you could live your life over? Then relive it again. And again." Excellent. It should be a movie or a limited series.