This is a hard one, guys. 
 I can't decide if this is a terrible book or an excellent one. I'm not going to give it more than 4 stars; conversely 3 seems too low. I am both disgusted by it and impressed. 
 As it has quite a few negative reviews here I thought I would start with my positive impressions (although, as you will see, they are all tangled up with each other). 
 Firstly, the book impressed me. I thought it was clever at times. I've read fantasy reasonably solidly for reasonably my entire life, and The Magicians surprised and delighted me at times with unexpected twists and reversals. I never knew what to expect going around the corner, and that unsettled me. I disliked this book intensely at times, annoyed that my expectations going into the book were being disrupted and corrupted. Harry Potter and Narnia? The only connection to Harry Potter that I saw was that they were students at a school of magic, which isn't particularly unique, so I would recommend not approach the book as "Harry Potter for adults" (I would say, on that note, that Harry Potter is probably more mature and adult in writing and emotional content than The Magicians ). 
 On the topic of maturity: granted, Grossman throws in random gratuitous sex, violence, and profanity quite liberally -- that does not make this book 'mature'. It reads more immature, which works and I will support to an extent because it is written from a particular viewpoint, that of a not-very-mature teenage boy with a bad case of ennui and anger management. The voice in this book is spot on... unfortunately for the novel, the voice is really very unlikeable. I cannot particularly think of a time when I liked Quentin Coldwater, even in the very beginning. Towards the end I liked him slightly more, oddly, as I finally felt he had undergone some emotional change, some evolution of any kind. For most of the book I found him cowardly, crass, dislikable, boring. I read as much as I could for the other characters and, as I said before, I enjoyed the moments of unexpected twist and creative use of fantasy elements, even if simultaneously the book annoyed me for not catering to my expectations. 
 This has become a very disjointed review so I will try to wrap up here.. the book is needlessly graphic, but in a very shallow, banal way, almost not worth getting angry over. Everything is well written from the protagonist's point of view, so it's a shame that he is so dislikable -- yet at the same time, the adventure told from the point of view of the miserable angry cowardly character was interesting, not least because he really wasn't the hero or even the hero's sidekick at all. He was just the narrator, and a grumpy one at that. 
 At the same time I am loathe to leave this as a 'do not recommend, avoid'. At one point I truly genuinely believed the book had ruined my childhood, and I was grim-faced for most of the last 100 pages; but I did not put it down. The book gripped me in the last sections and I had to keep reading until I finished it. Sequences of battles and ritual magic, as mentioned in a review below, are done well; the adverse, uncontrollable, scary side of magic is explored and gutted out. People die and get injured, gruesomely. Again: I was affected by this book. It bothered me, annoyed me, and I disliked it. But am I going to read the next two? Absolutely. It succeeded in gripping me and convincing me to read something I had an adverse reaction to. 
 So, read this because it really is an interesting read, if you can get past Quentin's utter dislikability, the somewhat wearisome and mocking 'reversal' of the fantasy genre, and the jarring upheaval of Narnia's influence and memory ripped into by explorations into the darker, more gruesome side of magic and magical escapism. There are , ultimately, some engaging observations about magic and human nature to take from this book, and I would read it for that.