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.
YMMV: The Professional
Complete Monster: Stansfield is such a manic psychopath that even his own men are afraid of him. He thinks nothing of killing a family, including the children, for shits and giggles while listening to classical music. Even though he seems upset about his henchmen killing Mathilda's little brother, he is really more worried about answering to his superiors for killing the little brother and his compassion seems to be more about finding out who sent Mathilda. Also, his voluntary going through lots of pills is to be taken into account, for any emotions he shows might be because of his wild, drug-addled mood swings. When one of his henchmen responds with disdain after the little brother is killed, Stansfield himself seems to have no concern one way or the other. As he later puts it:
Stansfield: It's always the same thing. It's when you start to become really afraid of death that you learn to appreciate life. Do you like life, sweetheart?
Mathilda (whispering): Yes.
Stansfield: That's good — because I take no pleasure in taking a life if it's from a person who doesn't care about it.
Narm: Léon's slow motion, cross-eyed yell right before his room gets hit with a grenade.
Special Effects Failure: Stansfield discovers the grenades in Leon's vest. Cut to outside, where one of the cars blows up before the explosion happens in the building itself.
Tear Jerker: Léon's death. A rewatch of the movie (and a reminder of his status as The Woobie) only makes it worse.
The Woobie: The main characters. Léon especially, who even as a hired killer, behaves rather childishly and innocent. He drinks milk, waters potted plants and watches old musicals with the look of a fascinated boy.