I read this as a freshman in college on a dare. A friend had been teasing me about my inability to read horror novels, so I caved and read this in exchange for a promise that he'd watch the movie with me after. My reasoning was that my imagination is scarier than anything they can put on film, so seeing the movie would take away much of the scariness.
I ended up totally loving this. Of course it freaked me out (I'm a total scardy-cat) and I'd never been more grateful to have roommates than when I could rush out after scenes like the bathtub scene and have people help me bring my imagination back under control. (I'm still unable to leave my shower curtain closed, though... afraid of what might be behind it :P)
The mind that created this fascinates me. So creative and so, so creepy. The ability to play on common fears and to turn it into an exciting, enthralling story was remarkable.