When I was told to read The Magicians, it was explained to me as "Harry Potter for grownups." Which isn't inaccurate, and I guess that Harry Potter is probably the more likely to have been read comparison for people of my age and younger, but I found it to be much more like "Narnia for grownups." The magical school stuff is in there through the first half of the book, but the focus seemed to be on setting up the worldbuilding and main characters. When we get to the Narnia portion, The Magicians reads quite well as a direct response to the series. 
 Perhaps the best way to describe the novel would be "Narnia, with a touch of Harry Potter, but where the characters are terrible people." Because "for grownups" is just a nice way of saying that the main characters will lash out and do terrible things for petty reasons, and there will be no redemptive nobility at the end. 
 Reading through some other reviews, I can see a lot of people didn't like this book because they didn't like Quentin, the main character. I can certainly see how they might respond that way - Quentin makes terrible choices, acts out for petty reasons, and then goes on relentlessly about his feelings of guilt. Under many other circumstances, I would have reacted the same way, and I've certainly complained an awful lot about books with terrible characters. 
 But, for me, it was okay here. I could read about Quentin's latest hurtful lashing out because the narrator never once made excuses for him. When I judged Quentin, the narrator judged Quention. I was asked to understand, but I was never asked for forgive or overlook. That's something that many books - even those deliberately setting out to write flawed character rather than accidentally creating them - have trouble negotiating. 
 I can see how that may not be enough, though. Watching Quentin train wreck his life over and over again was difficult and frustrating, even with the narrator's commiseration. Which raises the important question: Is it necessary to like the main character? 
 I think John Green addressed that beautifully when he said: "I don't know where people got the idea that characters in books a supposed to be likable. Books are not in the business of creating merely likeable characters with whom you can have some simple identification with. Books are in the business of crating great stories that make your brain go ahhbdgbdmerhbergurhbudgerbudbaaarr." 
 The catch, of course, is that there has to be enough going on in the story to make your brain go ahhbdgbdmerhbergurhbudgerbudbaaarr. At which point, we're looking at an issue of personal taste. For me, The Magicians worked, but I can understand how others might disagree. 
 Back to the comparison to Narnia, it's hard to imagine that The Magicians wasn't a response to the series. I didn't read the books as a child and, when I decided to tackle them as an adult, I decided to go in chronological order and only got through The Magician's Nephew before I got distracted by shiny things. But even just with that book, it was hard not to see the connections (the talking animals, the "hub world" with many pools through which one plunges into different planes, the witch who controls time/seasons, etc). 
 The commentary even gets quite direct in the second half, when the characters go to Fillory. At one point, a character explicitly tells them that they came looking for a child-friendly adventure, one in which they get to become kings and queens and perhaps fulfil their character arcs. And this character tells them that Fillory is its own world, it exists independently of the children who come to it, and it does not exist merely to cater to their desires. That was definitely a ahhbdgbdmerhbergurhbudgerbudbaaarr moment that made me appreciate the Chronicles of Narnia from a different angle. 
 It was interesting to read this at the same time as the Fionavar Tapestry, because the response to Narnia fits Fionavar just as well. Both The Magicians and Fionavar give us flawed characters who enter a new world - but while Fionavar takes the Narnia approach (an oddly naive position given the kinds of things that happen in the series) of having the characters "step up" and unleash the inner nobility that they couldn't find expression for in the mundane world, Grossman wisely concludes that people do not suddenly change with the scenery. Take a restless, never-satisfied, selfish jerk and plunk him in a magical world and he will still be a restless, never-satisfied, selfish jerk. Real change simply does not happen that fast, or that painlessly. 
 For all that ranting, I'm not actually sure how I feel about The Magicians yet, or whether I will be interested in pursuing the rest of the series. Quentin was very unlikable - and while that was okay in the small dose of one book, I'm not sure that I have the emotional energy in following through his entire character arc (wherever that may lead). It's the same reason why I gave up on Breaking Bad in the second season - I can see that it was a very well made show with a lot of interesting stuff going on, but it was just exhausting. 
 The strength of The Magicians is in its commentary on Narnia (and similar books). I get the feeling that Grossman must have grown up with the series, or at least loved it very much, because the criticisms never felt hateful. They were just insightful, and they contributed to how I perceive the series. 
 For weaknesses, the series took a very long time to get to the nougaty centre. We had to go through Quentin's entire magical education in episodic fashion before I had any idea why it should have mattered. Harry Potter did something similar, but the episodes there were so whizz-bangy that they sustained themselves. In The Magicians, Grossman was clearly struggling to balance the wonder of introducing his magical world building with the fact that his main character's defining trait is a sort of dissociative ennui. 
 That said, I'm at a loss on how the issue might have been corrected. The Fillory portion of the story could not have sustained an entire novel, and much of it needed the Brakebills background to work correctly, but making the Brakebills section of the novel more interesting would conflict with the character exposition. Elements were introduced and then immediately dropped, uncharacteristically, because Grossman clearly wanted to save them for later. I suppose a little more foreshadowing could have been sprinkled in, maybe the appearance of the Beast could have had more of an impact, but what there was (and as subtle as it was) worked so well once it all began to fall into place in Fillory. 
 I would absolutely recommend this book, but with the caveat that the main character has few redeeming qualities.