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.
Scrooge's anger and bitterness towards Christmas. Given the lifetime of tragedy he's suffered, with nearly ever bad thing in the course of his life happening to him at that time of year, who wouldn't hate the holiday after that?
Also the Ghosts in general, is the Past another Good Is Not Nice spirit trying to teach Scrooge about his past, or a Jerkass who really loves to exploit the flaws of Scrooge's past and in some versions show what he could've had if he was not greedy; pushing him away from loving Christmas due to regret, and enjoy it as he/she/it invaded his mind. Tends to depend on the adaptation though, as some versions of ghosts seem more benevolent than others.
Anvilicious: But good! (Apparently Dickens even considered "The Sledgehammer" as a title.)
While the moral of charity and giving is obvious, more specifically, the novella was meant as a Take That to Thomas Malthus, whose warnings of overpopulation resulted in laws that Dickens hated because he felt they hurt the poor.
Designated Villain: Scrooge. We're meant to see him as a villain because he's collecting money that he's rightfully owed on Christmas, while the people who owe him plead that they shouldn't have to pay simply because it's Christmas and they've spent their mortgage money on presents. No businessman would stay in business if he didn't collect. He also gives Cratchit Christmas day off work, but only after grouching about it.
Despair Event Horizon: Scrooge is dragged kicking and screaming over it when he is shown Tiny Tim's death and his own forgotten grave.
Magnificent Bastard: Scrooge and Marley earn this in the 1951 version. They offer to bail the Mercantile Association out of the debt caused by Jorkin's embezzlement, provided they'll be allowed to buy up 51% of the total stock. They'll only save the company if they can become the company, and both look really pleased about it.
Moral Event Horizon: The three spirits make Scrooge himself go through his past to realize how far his actions have gone.
Nightmare Fuel: Really, anything to do with Marley. He's not exactly a comforting sight to begin with, wrapped in chains and pretty dead-looking as he is; he visits Scrooge in frankly terrifying circumstances, scares the crap out of him, and tells him about the horrific fate in store, which he is already suffering.
The Ghost of Christmas Past in particular tends to get hit with this. This could be because the description in the book is virtually impossible to depict visually, other than via some form of animation(either conventional or CGI); the first paragraph of the description is fairly doable, but the second paragraph...
"... its belt sparkled and glittered now in one part and now in another, and what was light one instant, at another time was dark, so the figure itself fluctuated in its distinctness: being now a thing with one arm, now with one leg, now with twenty legs, now a pair of legs without a head, now a head without a body: of which dissolving parts, no outline would be visible in the dense gloom wherein they melted away. And in the very wonder of this, it would be itself again; distinct and clear as ever."
Uncanny Valley: The land from whence Mr. Zemeckis draws his CGI characters.
There was some improvement over his previous efforts (The Polar Express in particular), but he did tend to re-use faces for several characters (compare Fezziwig and Bob Cratchitt), and in one scene (in the future, where the Cratchitts are mourning Tiny Tim) the eldest son's face freezes after he's done with his lines.
Values Resonance: Part of the reason why this story continues to be adapted to this very day.
WTH, Casting Agency?: This blogger points out that pretty much every version of the story that gets told with existing characters has one in-story character that there's no good fit for, and one actor-character that there's no good role for, so they just squish them together.