Atlas Shrugged is a good book, definitely entertaining and thought-provoking. With over 500 reviews here, there's not much I need to add to that. Although I don't like this book nearly so much as I did when I was 18, I still think everyone should read it.
My criticism of the book and of Rand's philosophy of Objectivism(the two are nearly inseparable) is that the psychology and the relationships are entirely divorced from reality.
If you're inclined to use Rand's characters as models for your own behavior -- something that's at least as bad as modeling your manners on those of sitcom characters -- then check out "The Benefits and Hazards of the Philosophy of Ayn Rand: A Personal Statement" by Nathaniel Branden. This essay is posted on the web.
Like a lot of people, I read Atlas Shrugged -- and all Rand's other fiction and non-fiction -- while young and so was provided with an outlet for my teen angst and with fuel for those all-night bull sessions in college. (Kids without jobs, and philosophy professors with jobs, can debate for hours whether or not the world exists.) Atlas Shrugged and The Fountainhead also gave me a lot of silly ideas about dating that I fortunately outgrew. And when I got to the business world, I learned just how unreal Rand's world is.
A lot of people who read Atlas then decide that they also are misunderstood geniuses and act accordingly. Like Rand's characters, they imagine themselves to be absolutely right and the rest of the world to be absolutely wrong. I witnessed one Objectivist applying this to his job. He was smart and competent and young -- and convinced his way was the only way. He refused to listen to his coworkers, his bosses or his employees. He treated them all the way Rearden would treat any "looter" foisted on him in his own company. And, although his manager tried for a long time to teach him to deal with the real world, he ultimately found himself shown the door. He was still convinced that he had been absolutely right. For how could he possibly have anything to learn from other people? What was the point of listening to all these dimwits with their stupid ideas? Like John Galt, he was a law unto himself.
A few reviewers have mentioned how disgusted they were by the "rape scenes" in the novels. Most of these scenes are just consensual rough sex, except for the Dominique/Roark scene from The Fountainhead. Here again is an example of how Rand's characters fail to translate to real life. In the novel, the sex was NOT rape. Roark did a bit of quick mind-reading and untangled some complicated psychological problems in order to free Dominique's warped love and sexuality. (In Rand's novels, "no" really does mean "yes.") Like I said, this does not apply to real life.
Most of Rand's sex scenes are adolescent and laughable. I'm sure the editors of Cosmo would love to know Dagny's secret to (can I say this on Amazon?) never-fail simultaneous orgasm. Then again, those often produced post-coital philosophical speech-making by the men so maybe it's better left undiscovered.
"Love" in Rand's novels is equivalent to hero worship. This is fine if you take the novels as allegory, but not if you take them as realism. Rand intended her characters to be the latter. Dagny is in love with a man before she's ever met him, because he's the most brilliant mind to exist this century, if ever. Never mind such things as personality or compatibility. He's the greatest man in the world and she's the greatest woman, therefore their response to each other must be love. (This, incidentally, is how Rand justified her adulterous affair with Nathaniel Branden.) Instead of finding their own loves, at least other three men are left to pine for Dagny for the rest of their lives. She represents their highest value; how could they love another? (Branden moved on.)
In short, you'll be missing a lot by NOT reading this book. But you'll miss even more if you decide to mold yourself into a Rand character.