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.
Ear Worm: The swans' theme. You know, the haunting, twisting, minor-key oboe piece that just seems to fit dreamlike, beautiful, moonlit girls in a hopeless situation?
Ensemble Darkhorse: Odile has the vaguest character out of the entire cast and is little more than a plot device, but she is one of the most famous characters regardless, particularly after a certain film made note of the role. It doesn't hurt that she has probably one of the most difficult roles ever choreographed in ballet, involving 32 fouettes in a row.
What an Idiot: Prince Siegfried. You'd think he'd notice how "Odette's" dress is a different color than usual or that the person bringing her in looks suspiciously like the evil sorcerer.
The 1983 anime is even worse about this, where Odile tells him her real name and he still thinks she's Odette.