These are what we call the 'YMMV items.' Things that some people find in this work. We call them 'your mileage might vary' because not everyone sees these things in the same way. This starts discussions in the trope lists, a thing we don't want. Please use the discussion page if you'd like to discuss any of these items.
YMMV: The Magicians
Big Lipped Alligator Moment: At the end of the Brakebill welters tournament, Quentin experiences a revelation about things that don't matter, throws the match, picks Alice up, and jumps with her into a pool of water of unknown depth. None of this is ever mentioned again.
Complete Monster: Martin Chatwin, who's prepared to murder, mutilate, torture and consume his enemies just to keep his stranglehold on Fillory. And these "enemies" are almost entirely helpless- especially Professor March's class, who remained frozen in time while awake and conscious just because Martin felt like screwing with them. And when one of them dares fight back, he eats her alive.
Reynard the Fox in the sequel. He casually murders a room full of people then rapes the heroine as her friend watches on helplessly.
Family-Unfriendly Aesop: One of the major themes of the series seems to be that human beings are not psychologically prepared to deal with a world in which magic is real.
Nightmare Fuel: When time stops still in the middle of class and The Beast appears, though they can't move, everyone is still aware of what's happening, which means that Amanda Orloff was perfectly conscious the entire time she was being eaten alive one bite at a time, and probably a few people had no choice but to watch it all. The Beast counts as this in general.
The Woobie: Quentin (at least in the early chapters), Alice, and at times Josh.
Jerkass Woobie: Quentin drifts strongly towards assholish behavior in some chapters, but he remains consistently pitiable because a lot of the assholish behavior is rooted in his own psychological issues.
Stoic Woobie: Elliot, as Quentin comes to discern, has a very hard-won outward coolness.
From Bad to Worse: At the end of the first book, Quentin finally gets a solid reason to be a woobie and suffers an extended Heroic BSOD after Alice dies fighting the Beast. Qualifies as a Tearjerker as she is gone before he can tell her what he's realized - that he really loves her.
Unfortunate Implications: Apparently, getting very physically, very brutally raped by a ten-foot fox-deity on the much darker side of the Trickster Archetype spectrum is one way of gaining the power to turn into a beautiful, otherworldly demi-goddess.