I read the book when I was still a right-libertarian, and I credit it with playing a significant part in pushing me left into Anarchism. Thus, I'd say I fall pretty firmly in the camp of "I have read the entirety of Atlas Shrugged and severely disagree with it".
And I have to disagree with the "not an academic treatise" take: the book is a statement of philosophy first, and a story in a distant second. Most character's actions serve to either portray the "right" behavior of the Objectivist Ubermenche, or act a strawman foil to the heroes of the story. Frankly, the most surprising thing is that Rand doesn't stick to easy slam-dunk wins against her strawman "collectivists": she portrays the kinds of monstrous actions that her philosophy encourages, and then celebrates them. Franscisco D'Antonia's bombing of his own mine when he inevitably lost the fight against labor, the reverse-Robin Hood character's outright theft for the benefit of those who really don't need it, heck, the bizarrely rapey sexual encounters between Dagny and Rearden are all portrayed in a unquestionably positive light, and that's probably why so few people who don't already agree with the underlying philosophy finish the book: it's seriously alienating to see evil unambiguously praised.
Atlas Shrugged does not simply "inspire" individualism: It demonizes anything less than overtly selfish behavior, to the point of praising characters for acting against their own interests simply out of spite towards those who fail to live up to the Ubermenche ideal. Contrast that with individualist anarchist writers like Max Stirner, who's philosophy follows something like "Liberation begins with the self, but we can work better together": The former is destructive, where even self-interest takes a back seat to the rejection of cooperation, whereas the latter truely puts self-interest first, acknowledging that cooperation often grants greater benefit to ourselves as well.
As a novel, it's low-effort, monotonous wish fulfillment accented by the occasional romance or absurd moment. As a philosophical statement, it's a lackluster re-framing of the least favorable parts of Nietzche with the overt "Woman only get into academia if they're sterile" sexism being replaced with a more subtle "Women should be more like men" form. The book has few redeeming qualities, and can only really be enjoyed by a reader who already agrees with the premise.