Fleeting Relevance’s review published on Letterboxd:
I liked Nocturne but I can see why it's not doing so hot on here. I'm an only child, mind, but the central sisterly relationship never felt even remotely believable to me. Juliet and Vivian seemed more like friendly acquaintances who became rivals, not freaking twins, and it doesn't help that the parents hardly factor in at all.
Another issue is that Juliet's bursts of bitchiness towards her sister and the rest of the human race come across as totally unnecessary and almost comically petty. Her primary driving force is also unclear, like obviously she wants to be successful but she also seems to just enjoy screwing over other people and I never quite got a grasp on her motives. These problems are compounded by what I think is the film's biggest weakness: the dialogue, which occasionally drops to the level of pro-wrestling promos... okay maybe not that bad but still not great. I definitely like this movie better when it doesn't talk.
And when it's not talking it has some good things going for it! There are some screenshot-worthy visuals here, some cool use of music both classic and modern, and Sydney Sweeney totally held my attention. She has this 'timidly dangerous' vibe here that put me in mind of Elle Fanning in The Neon Demon, one of my favorite performances in one of my favorite films. Honestly I think Nocturne would make a great opening act for a double-bill with Neon Demon, and that's a damn hard movie to pair anything with so bonus points for that!