The Magicians is, on the surface, a mixture of Narnia and Harry Potter, but on a much smaller scale. The story follows Quentin Coldwater, a supersmart teenager living in our world, who fantasises about Fillory, a magical land written about by a writer called Christopher Plover, where several children accidentally travelled, had adventures and became kings and queens. Ring a bell? Only instead of Aslan, Fillory has two Rams as guardians.
So, one day Quentin follows a piece of paper down a garden and ends up in a place where he has apparently been invited to sit for an exam. His mind skips right around the absurdity of it all [which is also a sort of test] and aces the exam. And that's when we learn that he is at a school for magic [called Brakebills] and that he has the option to study it there, should he choose to. That's the Harry Potter association.
Quentin chooses to study at Brakebills [like duh] and eventually majors in Physical Magic, where he is grouped with four other young magicians. They become good friends and eventually, their path leads to a button - a button that takes you to Fillory [overload of Narnia at this point].
So far, it sounds like it's a glorified fan-fiction, and by God, it's hard to defend it from that accusation. But look at it like this: the book takes elements from Harry Potter and Narnia, but it transforms into something else. This is not a book for kids, though HP was dark when it wanted to be. There are more complex emotions that storm around the book. Things are not simple and straightforward and magic is not easy. It takes really brilliant people a lot of work to master simple things. For another, we are not going at it year by year with a neat little problem at the end.
The book is unflinchingly bittersweet. In many ways, it is the next step for the HP generation. You have learned magic, but there's nothing much to do. There's a sense of pointlessness, a frustration that addresses the core of our nature that hungers for fairy tales and fantasies, that looks for escapes in another world.