I got The Martian as a gift in paperback, but as most know by now it was originally posted online for free, then put out as a 99 cent Kindle edition. It went completely nuts, became a bestseller, and now he has a movie deal. I hear Matt Damon is going to play Mark Watney.
And everything the reviewers have said so far is true. I could put it down, because I'm disciplined (compulsive), but it was damn hard. I devoured every page. Mark Watney is a likeable, everyman/McGuyver. He logs his solutions to insanely hard survival problems with a great mix of stress and pride, and throw sheer joy of problem solving into the mix. This is true old-school Golden Age Science Fiction, where the science drives the story. The writing is matter-of-fact, the protagonist is basically the author, and it all works perfectly.
Andy Weir is a phenomenon now. I do kind of wonder what he's going to do with himself. I don't expect him to repeat this feat, and it would be painful to see him try. He does say he's been writing as an amateur for some time, but for him to do another commercially successful book he would have to get into more literary things like character creation. Hard to pull off. And who cares. If this is all he does, he's gone a ways toward reviving hard SF.
I give it 5 stars. And this is not an Amazon 5 stars. I've only given that a few times out of the 1300+ stories I've reviewed. It is a masterpiece of its type. I noted that it did not get a Nebula nomination. If it doesn't get a Hugo nomination then SF awards are simply broken and I will have a hard time justifying paying attention to them anymore.