I enjoyed the language and the world of the Magicians, but I was left cold by the lead. Quentin was a privileged git who was realistically sketched, but who angered me with his judgmental moping. He's still the lead, but now that he's become one of the four rulers of the magical alternate dimension of Fillory he's actually grappling with how he should live his life rather than bemoaning his failure to find happiness. He also shares this story with the extended flashbacks of Julia, a childhood friend he left behind when he was accepted into the arcane boardinghouse Brakebills. She is now also a Queen of Fillory, but hers was a black market education, attained through hustling and without the safeguards of the academy. While her story is not without happy moments, the end of the flashback is enormously dark. The end to the book I will not spoil, but I found it far more satisfying than the ending to the Magicians which notably suffered in its final chapter.
In enjoying the end, I disagree with Alyssa Rosenberg (important spoilers abound) who has an excellent suggestion for a narrative change to the final chapter, but finds that Quentin's changes are largely derived from Julia's suffering in an old and unfortunate trope. I think multiple reasons are established, but I don't have much to add beyond what I put in the comments on her blog.
I would recommend the book to anyone who enjoys Grossman's writing and characterization, even if they weren't fond of some of the characters in the Magicians. The thornier question is do I recommend the pair of books to someone who has read neither? While my endorsement isn't as strong as Moti's, I'm going to go with a hesitant yes for fans of modern world fantasy and stories that lean heavily on the interior lives of their characters. On the latter point, it may be simplest to just check out the first book and read a chapter or three. If you don't get the urge to quote lines to other people in the room, then put it down and don't look back.
Source: Recommended by Moti and checked out by Kate from Howard County Libraries, thanks to all three.