I wasn't planning on seeing the movie, but until recently, I had been really pumped to read the book, as I've seen huge amounts of praise for it. I even had several friends recommend it to me. How often do you get book recommendations from friends? (I never do, that's for sure).
About a week ago, I got the chance to read some sections and sample it. For all the hype, this was my first time seeing the actual text, and damn. The dude's prose was incredibly bland, the constant awkward internet humour in a novel was awful, and the character just seemed like an ass.
Reading others' comments since, I've seen a considerable minority of people echo what Chino said. For all the science geeking out, there's no depth to it whatsoever. While stranded on Mars for years, the main character doesn't change in any way, he isn't psychologically affected, and he never experiences a profound thought.
Basically, I'm REALLY glad I sampled it before buying it.