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.
The New 52 was this for the character, effectively declaring Brightest Day and The Search For Swamp Thing non-canon after the mini-series killed off Swamp Thing in favor of Geoff Johns's hack decision to invalidate the Alan Moore version of the character by killing off Swamp Thing as written by Alan Moore and replacing him with Alec Holland, who is resurrected SOLELY so he could be turned into Swamp Thing via deux ex machina.
Even Alan Moore attempted to back peddle (or sidestep the issue since) with his retcon of Swamp Thing's origin by essentially having Abby and everyone else still treat Swamp Thing as Alec Holland. Later writers essentially took the stance that Swamp Thing, for all intents and purposes IS Alec Holland, insofar that he's a plant clone of him with all of his memories and personality, even if the real Alec Holland is dead.
Complete Monster: Anton Arcane is a Mad Scientist turned Evil Sorcerer obsessed with immortality and its secrets. First seen attempting to steal the Swamp Thing's body, Arcane failed and died in the attempt. His soul, however, returned from hell to steal the body of his niece Abigail Arcane's husband, Matthew Cable. In the guise of Matthew, Anton raped Abigail and consigned her soul to hell in his place. In his new position on earth, Arcane attempted to drive reality itself to insanity, using the souls of resurrected serial killers to cause destruction as the innocent succumb to savage, homicidal urges.
In the New 52, Anton Arcane's new incarnation is a being of boundless cruelty. In his pursuit of immortality, Arcane took over the elemental force of The Rot, the natural force of death and decay and subsumed it to his will. Arcane extends the Rot to devour all that lives and trap the world in deathless limbo he can rule. Arcane even forced his own nephew to be the Rot's avatar, devouring his mind from within. In Arcane's battles with Swamp Thing, Alec Holland saw a future where Arcane gruesomely tortured and beheaded Abigail and saw lobotomized clones Arcane had made of her as cannon fodder.
Fanon Dis Continuity: People tend to view the series solely in terms of the Alan Moore run, which may partly be due to the fact that the rest of it has either never been collected in trade form or is otherwise notoriously difficult to find. It's generally accepted that the Wrightson-Wein run is pretty good and that the tail end of the Plasko run is required reading to fully get the Alan Moore run, while the Brian K. Vaughan run...isn't.
Doug Wheeler's run often falls into this almost by accident, since it was the only run to be utterly forgettable. Even with the benefit of hindsight it doesn't really have any fans.
Nancy Collins' run has its share of (mild) detractors due to the fact that she basically reset the series back to the end of Alan Moore's run with a Swamp Thing that was (relatively) mainstream-friendly and akin to the Wrightson/Wein and Plasko runs, as she concentrated more on Character Development and an expanded supporting cast than horror.
Mark Millar's run too falls into this line as well, given his character derailment, and the fact that it later came out that much of it was plotted (uncredited) by Grant Morrison to give the inexperienced Millar a leg up in the industry.
Brightest Day and The Search For Swamp Thing were declared non-canon by Swamp Thing fans for the way they scorched earth EVERY Swamp Thing story written (as well as "The Anatomy Lesson") in favor of Geoff Johns going all "Captain Yesterday" and basically resurrecting Alec Holland simply so he could die again and become Swamp Thing FOR REAL and KILL THE ALAN MOORE VERSION, WHO WAS DESCRIBED AS BEING A CORRUPT PARODY OF SWAMP THING (granted, because Swamp Thing had been possessed by a Black Lantern Ring). Thankfully, the New 52 flat out erased this from canon with the two books having been erased from canon.
Love It or Hate It: The Brian K. Vaughan run. An almost entirely unsympathetic yet often fascinating main character on a rambling road trip, with only token appearances from her father? Opinions are still strongly divided on this volume.
Invincible Villain: Arcane during the New 52 with new re-imagined Rot based powers that allow him to instantly kill, turn undead, and take control of any living thing that has even a single dead cell in it, anywhere in the entire world at any time. There are no functional limits to this power, only that champions of the Green and Red can sometimes resist it, but even then Arcane can just steal somebody's appearance and kill them before they can attack. He is also effectively unkillable as he can just reform a body from any corpse. Add to the fact that he's been around for centuries, effortlessly killing champions of both the Green and Red, until finally infecting and taking over the entire world in the Rotworld segment along with killing and cloning Abby. He only loses not through any action of the heroes, when he's declared to be TOO successful as a villain, and the Parliament of Rot withdraws their support and allow them to rewind time to before his victory.
Moral Event Horizon: Swamp Thing's daughter Tefé burns through all audience sympathy when she enforces a Sadistic Choice on a man who started a forest fire, forcing him to choose between the life of his daughter and his wife. She doesn't kill anyone, but his family get to see him choose.
My Real Daddy: Len Wein helped create Swamp Thing (and more), but Alan Moore's complete rewrite of the character is the one that lasted.
Squick: Anton Arcane, especially after he possesed Matt Cable's body.
In limbo at the time. Ivy was pretty much a D-List Batman villain at the time as it was not until Batman: The Animated Series that she was able to garner enough popularity to be considered a big time player.