Rand is hated in philosophical circles because she is a pop-philosopher, her philosophy is not well-founded, and her philosophy is centered around her, not around its ideas. Rand is hated by everyone else because she was a homophobe, scientifically illiterate, and annoying as hell to read:
Rand is consider a pop-philosopher in the most derogatory sense. While philosophy majors might scoff at Fight Club as pop-philosophy, it doesn't make any overt philosophical statements... But Rand does. Objectivism, the philosophy of much of Reddit's ire, was first illustrated in the Fountainhead, but then it blossomed in Atlas Shrugged. In Shrugged, the climax of the book is a 60 page novella outlining the philosophy and its so-called axioms.
So, just from that we can understand that when one says, "Rand is pop-philosophy" we mean something very different from other bemoaning of philosophy. Schopenhauer said Hegel was a pop-philosopher, when Sagan made Cosmos he was considered a pop-scientists. These are still insults, but when we label Rand a pop-philosopher we mean it in the sense that she removed herself from the realm of journals and established peer-review systems.
This, is indeed, the big reason why we know that Rand's philosophy is not well-founded without me even having to walk to my book shelf. As far as I can tell, she didn't publish in major philosophy journals. She didn't take criticism well. Her works existed in an echo-chamber, and the only other voices that she would respond to were those that she let in. Indeed, if you look at the organizations made to evangelize Rand, they have fights and break ups all the time. Why? Because they're not allowed to change their canon! The Canon is serious business for an objectivist. It includes all Rand's books, the  Ayn Rand Lexicon (because, apparently, she needs her own dictionary), and many of the writings by Leonard Peikoff, who is sort of the objectivist Vicar of Rome.
 (1)tl;dr: Major philosophers don't like Rand because she didn't interact with them, lest her ideological purity be tainted.
Most people who are lucky enough to think about philosophy too much, don't like Rand for a number of reasons:
She is a homophobe:  > "[same-sex relations are] immoral, and more than that; if you want my really sincere opinion, it's disgusting." (further source)
Objectivism also turns out to be surprisingly scientifically illiterate. Many of her followers have said that general relativity and quantum physics are bunk theories because their philosophies disagree with it.  Rational Wiki does a great job listing these conflicts with the natural sciences.
Some Objectivists like David Harriman and Leonard Peikoff seem to have a problem with modern physics, especially quantum mechanics due to its probabilistic nature. The breakdown of classical mechanics-style causality at the quantum level doesn't square with Rand's vision of causality. This has led to declarations by Objectivists that modern physics is "corrupted" or "tainted" by a "Kantian influence"If the readers from DepthHub may excuse an outburst, what the flying fuck? Tainted by Kantian influence? ... sigh... who is John Galt?
Anyways, she even messes up the social sciences: reread Galt's speech, and go ask  /r/psychology if she got any of the concepts right: She didn't. Why? Well, according to  Clemson University's Robert L. Campbell, Rand made a* "declaration that philosophy in no way depends on psychological theories or findings."* Well, I say, and most people agree, that is bullshit. The empirical evidence is highly in favor of cognitive (along with biological) psychology. Her psychology is Freudian and non-scientific.
And, finally, we get to her books. You said yourself:
I found the books a bit tedious...Because they are! The characters are boring, and the rape-scenes are awful. Galt, the Christ-figure of Shrugged, is the flattest character in existence before Twilight's Bella, but at least one can make the argument Bella is intended to be that way to get horny tweens to buy the book. Galt is flat because, apparently, idealized figures in reality are supposed to be flat. For you people who didn't take AP English in high school, a flat character is some character that is a stereotype, that doesn't change, and has no real growth. Thats why I say Galt didn't have real growth: a perfect man can't grow, because he's already perfect, which makes him a shitty character. Harry Potter, Frodo, Jason Bourne, Neo-- all these characters had philosophical, spiritual, and mental growth. Galt has none of that.
(2)tl;dr: Her philosophy is bad, her books are bad, and she should feel bad (but hey, she's dead).
(side note: A lot of her hero characters are engineers/architects/technicalpeople. This is Roark, Henry, Dagny, Galt, and Francious. The hero of Anthem is a natural electrician. This might be why our hacker friend geohot might be interested in Rand).
Edit: Fixed some part I thought where bad. Added some more discussion about flat characters. Extended Objectivism's scientific uncredentials.