Plenty well enough has been said about this story (and its pending film) already. By the time I received the book for Christmas in 2014 (at which time I had never heard of it), it was already quite a phenomenon. With that in mind, here are a few thoughts anyway.
First of all, the publishing history of how this book came to be in its current form is an interesting story itself. This can be heard firsthand by Andy Weir over at the Inquiring Minds podcast—great interview, too. I must confess, I love to hear these “success stories” from indie authors who simply write something because it brings them joy, then they gain an online following that they weren't even trying for, then end up releasing something to universal acclaim. Hugh Howey comes to mind.
As to the quality of the writing in The Martian, it leaves a bit to be desired. Without meaning to sound condescending, it reads exactly like it what it is: a fictional narrative written by an engineer who could out-quiz the lot of us under the table. It is clunky in places, corny in even more places, and much of the character dialogue consists of typical, familiar tropes. Despite these things, Weir manages to pull off what is ultimately a well-paced and -developed plot, even if his phrasing is nothing original and his characters are fairly cookie-cutter apart from Mark Watney himself.
Watney is, for the most part, an enjoyable character (if corny at times), and I think he probably had to be a fun character for all the lengthy passages of oration detailing mathematical and scientific processes. Were he flat, many readers would probably give up by Page 20. Reviewers have praised the humor in this book, although to my ear it came off as eye-rollingly bad in places, chock-full of the worst pun-fodder your dad could ever come up with. But at least the author was breaking up the monotony that could have come from so many explanatory sections describing Watney's many survival tasks. Also, it will be interesting to see how much of the humor makes it into Ridley Scott's film, as Matt Damon may be just the actor who can pull off the sort of deadpan delivery to make such cheesy lines believable.
I found the most intriguing part of the book to be the lengthy descriptions of Mark's farming, repairing the HAB, regenerating water for himself, and all the hundreds of other things he must do to survive on Mars. From reading other reviews, I believe I am in the majority with this opinion. To the layman (referring to myself here), there is something so utterly foreign and fascinating about these space and physics concepts that Watney encounters, and it is even more mind-blowing to recognize that there are thousands of people working on these very things every day. The mark of Weir's writing talent comes through in that he was able to explain extremely complicated processes in such a straightforward, easy-to-follow way. And, goodness sakes, do some of them sound exhausting. There is a reason only a select few out of billions were ever destined to become astronauts.
In all, The Martian was an enjoyable read, even if it is not necessarily great literature (and granted, it has never claimed to be). What you'll get is a fast-moving space thriller surrounding a nugget of scientific research that is entertaining and—so the experts say—pretty close to accurate (or as close to it as Weir could get).