It seems to me, there are a number of issues with this book that may hamper readers from getting into it today. First, it probably is too deeply rooted in 1970's US counterculture and intelligensia. Sex, drugs and politics are heavily 1970's. Younger readers may not be able to identify with it (not all older readers will identify either). Not all older readers will want to revisit this. It has the 1970's mix of political paranoia and utopian hopes.
Not all readers will like the literary experimentalism. Parts of it are sort of "stream of consciousness". A lot of it just jumps around between character threads - like watching TV while someone else keeps changing channels. The bits you see may be interesting, but more like fragments than a whole. Here and there it inserts an explanation for non-Earthlings who may not be familiar with the primitive customs or details of 20th century US society. Here and there, you'll find some comments about quantum physics and its oddities. There's some good science, some questionable science, some questioning of religious / mystical beliefs, and some apparent acceptance of some other mystical or psychic beliefs.
We're presented with a series of alternative versions of Earth in the 1980's or so [the future relative to the writing of the book) - as well as alternatives of the decades leading up to that. Generally speaking, neither the individual alternative versions nor the collection of them all has the kind of culmination one usually expects from fiction.
It would be hard to present the book's plot as something that leads somewhere or to view it as having character development.
It could be described as SF as it consists of some novella length parts and some longer parts each of which contains some of the same characters and some common settings at what is supposed to be the same time period - but with differences in events and characters' lives. This is supposed to reflect different parallel universes or quantum probabilities. Some of the events also take place during a year after the year the story was written - and in some cases, it's futuristic. It's presenting a number of alternative versions of people and history. In addition to "alternative histories" there are also some "alternative worldviews" - that is, people whose conspiracy theories or otherwise unorthodox way of understanding the world presents an "alternative world".
Personally, i found my mind drifting off a number of times. And I lived through the 1970's, so that was not an issue for me.