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.
Complete Monster: Bill Sikes is one of the most vicious characters that Charles Dickens ever created. Sikes beats his dog, abuses his girlfriend Nancy, and uses Oliver, a young boy to further his criminal career, threatening to shoot him if he gives him away. His worst act is killing Nancy in cold blood when he thinks she betrayed him. He smashes her face with his pistol and when she begs for mercy, he beats her to death with a club, and keeps beating her when she's already dead. He later threatens to kill Charley Bates when he's on the run for Nancy's murder and he leaves Oliver for dead in a ditch. Other criminals fear Sikes and his violent temper and none of the other villains come close to matching him in being an utter bastard.
Karma Houdini: Noah Claypole saves himself from prison by selling out Fagin, and goes on to become an Informer because it's the easiest and safest job he can think of. So far as we know, he never stopped being The Bully or a Dirty Coward.
Monks may count. He does eventually get imprisoned and dies of a fit in his cell, but only after Mr Brownlow gives him half of Oliver's inheritance and lets him return to his criminal ways. No-one but Oliver and his friends ever learn that Monks was one way or another behind most of the criminal events in the book.
Also, Nancy, Charley and The Artful Dodger grabbing Oliver and bringing him back to Fagin's clutches. Nancy, however, ends up excused for this through virtue of having a Heroic BSOD when she fully realizes how screwed up this was, and openly calls Fagin out before collapsing out of stress.
Monks's biggest one is arranging to have his 12-year-old half-brother Oliver's life completely destroyed without real reason other than pettiness and jealousy. Specially marked when he takes the Orphans Plot Trinkets from Bumble and Corney and tosses them into the Thames so no one will ever be able to prove that Oliver is the son of Agnes and Edwin Leeford.
Nightmare Fuel: Nancy's death is horrifically violent; there's a reason why performing it drove Dickens' blood pressure right up.
Purity Sue: The whole Maylie family. Don't remember them? That's probably because they're among the first things to get cut from most adaptations.
To make matters worse, they seem to exist merely for Author Appeal, and the sections involving them can be almost entirely excised from the story without hurting the plot one bit.
Tastes Like Diabetes: The description of how Oliver started to live with the Maylies. A more sinister twist on this is how the parish people (Mr. Bumble even) openly play this trope to the hilt to seem caring to the outside world, and in truth are cold blooded assholes in private who'd just rather watch the poor die off in droves.
Tear Jerker: Nancy's death. Sure, it's incredibly melodramatic and horrific, but it's heartbreaking when, knowing she's about to die, Nancy pulls out Rose's handkerchief and pleads to God for mercy before Sikes strikes her down.
The character Fagin who is depicted as a Greedy Jew, something that wasn't that uncommon in Victorian literature, but since World War II has caused a lot of controversy with modern readers.
On the other hand, Dickens' vivid and social descriptions of the problems of the poor people in society were something that actually shocked 19th century readers, who weren't used to hearing about all this hidden atrocities.
The Woobie: Dickens' bread and butter was this trope. Oliver and Nancy are both examples.
Chafing at the antisemetic portrayal of Fagin, Will Eisner created wrote a comic in which Fagin is a misunderstood Anti-Villain. Or, to be more precise, in which Fagin has gone Then Let Me Be Evil to the world combined with what, if it had been published at the time Dickens wrote in, would have been rather pointed social commentary about the ill effects of limiting the career paths of an entire group.
Then Let Me Be Evil was also the solution to Fagin's characterization in the 1999 and 2007 miniseries. In fact, the 2007 version makes him relatively benevolent, and plays up the extent to which he is victimized by contemporary antisemitism.