When a book has had this much word of mouth, I tend to react by not wanting to read it, at least until the hubbub has died down, but I this case I decided to give it a shot and am very, very glad I did. 
 Andy Weir's novel is a rollercoaster ride of an adventure story, the pacing utterly breathtaking from the beginning when the crew of the third manned Mars mission are forced to abandon astronaut Mark Watney during a rushed evacuation, leaving him for dead. The trials Watney faces to survive - initially without any contact from Earth or his crewmates, and assuming they think he is dead - make this utterly gripping but what really carries the book is that, in Mark Watney, Weir has written simply one of the the most engaging characters I have ever read. And he has to be, as 90% of the book is carried by his personal log. Watney is inventive, witty, profane and profoundly human - possibly more upbeat than is realistic for someone abandoned 225 million kilometres from home, but the book is all about striving and surviving against impossible odds, so we can forgive it that. 
 Weir writes well enough to genuinely make us fear for Watney's survival as each subsequent mishap occurs, despite that fact we intellectually know he couldn't be cruel enough to write this and have his hero fail (could he?), and the other characters are all drawn excellently within their roles. While (perhaps) I cried out on occasion when some other disaster befell our stranded protagonist, these were certainly not overdone and the solutions by which he progresses always brilliantly inventive yet never stretched credulity by being superhuman, or even by being something on smart, motivated bloke (one of the sort of calibre you'd think would be required to be a Mars explorer) could come up with. I cheered for Mark Watney, and smiled and shook with fear and, regularly, laughed out loud. 
 All in all, if you haven't read The Martian yet you really should.