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.
Awesome Music: While occasionally unnoticed by viewers and having virtually no available soundtrack, the movie has what is arguably one of the most beautiful scores to be heard in a film. Notable examples are when the BFG makes the nightmare for the queen and when the BFG leads the RAF to Giant Country. Pretty funny, considering that one of the composers was one of the members of Herman's Hermits.
Ear Worm: The song "Whizzpopping" will get stuck in your head for hours on end. So will "Sometimes Secretly".
As with many a Dahl book (and movie adaption thereof), many a child can be traumatized by the Giants in the BFG. Oh, and nightmares are actually used as a tool in the book/movie.
The BFG's ears are so large, he can hear near anything. For example, when he picks a beautiful flower, he can hear it scream.
The first seven minutes or so of the movie (while containing a very awesome score) can be pretty freaking scary for some people. Not to mention the Fleshlumpeater-gets-child-in-the-night scene.
Sophie nearly getting eaten by the Bloodbottler is one as well.
Trogglehumpers are literal nightmares.
Heck, even the names of the giants alone are disturbing...
Paranoia Fuel: There exist Giants that can run anywhere in the world in a single night without being detected, in spite of their size. They reach through your window, snatch you from your bed as you sleep and eat you.
Uncanny Valley: Due to being rotoscoped, the queen, the Paras and the Royal Guards look very unnatural in the cartoonish setting of the story