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.
Alternative Character Interpretation: is Tris a brave, compassionate, sharp but self-doubting heroine who is worth rooting for, or is she an angsty, self-absorbed person with little human decency despite her upbringing, and some sort of constant mild concussion that blinds her to the bleedin' obvious?
Was Eric's eulogy to Al a sincere Pet the Dog moment, or was it a lie simply to make himself look good? While Tris thinks it's the latter, Living Lie Detector Christina didn't point it out.
Broken Base: The announcement that Uriah will be cut from the first movie and saved for the sequel. Some believe that Uriah's purpose in the first book wasn't that important, while others that love the character still call heresy on it. Basically, it's Tom Bombadil all over again.
The ending of Allegiant has severely divided the fanbase, with the reviews on Amazon averaging 2.5 stars.
Molly is described in-text by Christina as the kind of kid you'd see torching ants on the sidewalk.
Also, Erudite's leader, and the main antagonist of the book, Jeanine. She engineers a revolt against the Abnegation-ruled government by mind-controlling all of Dauntless, resulting in countless innocent people killed.
Fridge Logic: The worldbuilding is pretty vague and the social caste system in the society is rather simplistic and one-dimensional. Might be Fridge Brilliance in that the whole point of the story is to tear down such a system and demonstrate why it would not work.
Hollywood Geography: Dauntless territory apparently stretches from the Hancock building to Navy Pier, among other inconsistencies.
Mary Sue: It's one opinion on Tris, although it is emphasized throughout the story that she is hardly a perfect person.
Moral Event Horizon: Peter crosses this so many times, it's hard to keep track. Shining examples are how he stabbed Edward in the eye while he was sleeping. Then there was the time he hung Tris over the chasm (claimed it was just to scare her) and groped her chest, while mocking her.
For Caleb, betraying his family to the Erudite. The full information about the outside world and what Jeanine told him has yet to be disclosed. But regardless, it doesn't change the fact that he sided with the faction that killed his parents and helped with the capture and attempted execution of his own sister.
The Woobie: Four. He's actually an Abnegation transfer named Tobias who left because his father, Marcus, constantly abused him.
Al is arguably the biggest one in the entire series. He didn't belong in Dauntless from the get-go and only joined to make his family proud, when he clearly belonged in somewhere like Amity. His entire initiation experience is agonizing and terrifying to him, and he grows more and more distant until eventually, when it's clear that his only choices are factionlessness and death, he joins with Peter and Drew in their attempt to murder Tris, regretting it immediately afterwards. It gets worse when Tris coldly rejects his pleas for redemption, despite being fully aware of his mental state and the intentions behind his actions, which leads to his suicide. A major What the Hell, Hero? moment for many readers.
Tris, by the end of the first book. During initiation, she is bullied, verbally harassed, and sexually assaulted for being a "Stiff", becomes a victim of attempted murder, drives one of her friends to suicide, watches her entire world and society crumble around her, is forced to shoot one of her best friends (who was mind-controlled), loses both of her parents, and is nearly shot and killed by the boy she loves (who was also mind-controlled).
Trauma Conga Line: From the ending of the first book onwards, almost every character crosses this.
Unfortunate Implications: Smart people are inherently evil, and if anyone in your family is more intelligent than average they will betray you to other intelligent people.
Wangst: Depending on the reader, Tris's endless agonization over everything might be off-putting.