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: As a film about jazz (and the lengths to which one goes to perfecting their performances of it), this is to be expected.
Crazy Awesome: The editing and sound mixing really help to make the film's musical moments stand out as cinematically thrilling. The final performance is a true stand-out.
Crosses the Line Twice: Many, many of Fletcher's interactions with his students can make for this. He'll often call out his students on a mistake, and then compound on this by making fun of the student for either their nervousness or for a specific aspect about them, be it weight or their mother walking out on them.
Esoteric Happy Ending: The film ends with Andrew finally winning Fletcher's approval with his performance of "Caravan". Unfortunately, Andrew's self-destructive obsession to become "great" costs him almost everything in his personal life. This ultimately leads the viewer to wonder if him achieving greatness was really worth it, especially given the sheer amount of vitriol he receives from Fletcher up to the film's end.Damien Chazelle shares his thoughts here.
Family-Unfriendly Aesop: There has been a small debate on what the film's stance is on whether the film supports Fletcher's methods or not. His abuse has a terrible effect on the psyche of his characters to the point that one former student is revealed to have committed suicide from having endured so much under him. However, he does instill a drive in Andrew to better himself, and the final drum solo in the movie's climax shows that he was ultimately successful in his objective.
He Really Can Act: Those who either didn't see his work in The Spectacular Now or just regularly pigeonholed him as someone who could only play variations of the "frat boy" character archetype would be surprised at just how effective Miles Teller is as Andrew. He has to sell a lot of the character's vulnerability and determination, and pulls it off well. Additionally, much of the drumming in the film required his own preparation.
Magnificent Bastard: Fletcher. Luring Andrew into a false sense of security so that he could embarrass him in the film's final performance made for a devious reveal. Luckily, Andrew is able to save face with his drum solo.
Moral Event Horizon: It's not really a question of whether Fletcher crosses this, but when. If he doesn't cross this by lying about why one of his pupils died or when he mocks how Andrew's mother left him, then he certainly has near the endgame by tricking Andrew into joining his new band so he could humiliate him in the film's final concert.