Stand on Zanzibar by John Brunner
I've had a few false starts with this one. Finally made myself read past the first few pages and it has drawn me in.
Nearing the end and I am feeling like it deserves the Hugo it won in 1969 and its status as a classic of SF.
https://www.tor.com/2011/02/06/hugo-nominees-1969/ is a pretty good write up of what was nominated elsewhere and what might have been overlooked altogether. Looks like that was quite the year for SF.
Samuel R. Delany's Nova which got a nomination is definitely going on my to read list.
Also of note: Ursula Le Guin's A Wizard of Earthsea was eligible that year but somehow didn't make the cut for any of the awards. This one is a personal favorite and it's a bit disappointing to see it got snubbed. It gets classified as YA but is absolutely worth a read for people of any age. Definitely recommend sharing with the kiddos for those of you with fantasy inclined spawn.