I love the depth that the book goes into. The power and emotion that she pulls from all of her characters is amazing. Other than that, the imagery, though it contains amazing logical connections and overturns taken-for-granted socially assumed values, can get dry sometimes when I read through it. I listened to the audio books of both The Fountainhead and Atlas Shrugged, and oh. my. god. how much better it was after reading through half of Atlas Shrugged.
Personally, I liked The Fountainhead more. While most characters in Atlas Shrugged are either black or white (morally), the characters in The Fountainhead are on a sliding scale between the two poles, which makes for some really profound dynamics. The Fountainhead is the best book I've ever read (I mean listened to).
I was an objectivist for a while, especially after reading The Virtue of Selfishness