2.5 stars, rounded up
As a historical relic, Alas, Babylon is fascinating. Written just as things were heating up during the Cold War, it displays a level of paranoia that seems outrageous/laughable today, depending on your disposition. Still, I have no doubt it's accurate as a gauge for the mood of swaths of the public at the time (I'm old enough to remember the 80s from the "other side" of the world - in Bucharest, we lived in fear of nuclear fallout from any bombings unleashed on the USSR, and that was when the Cold War was winding down).
I actually enjoyed this quite a lot, but feel duty-bound to detract some stars for the record - first, as a book written about the deep south (Florida) pre-segregation, it's pretty blatantly racist (though not militantly so, at a time when violence against non-whites was common; in fact, Frank presents his white characters as tolerant, and writes about their solidarity with the black inhabitants of Fort-Repose. Still, this "tolerance" is quite paternalistic and thus, condescending; he's like those people today who "have black friends" so they don't consider themselves racist..). Second, ditto on women. Frank goes to some lengths to portray women as independent, yet in the next breaths pats himself on the head for being so forward-looking while restating how women still "need" men.
In both dimensions of race and gender, Frank probably was indeed "ahead" or at least in line with the times - he recognizes non-whites and women are people, have (or should have) equal rights, and should be treated with dignity, yet his very tone undermines his points. Like the white guy who says, almost surprised, "she's a woman, and she's so independent and strong" or "he's black, and he's so responsible and intelligent"...
Also, unrelatedly, the book is pretty superficial, mainly because it skims over so much time. It gives some idea of a new post-apocalyptic world, but there's not quite enough there to get a solid sense of the entire picture, and the reader is left craving so much more in the end.