Michael Sicinski’s review published on Letterboxd :
Neither outstanding nor horrid. It seems rather puzzling, though, that so much of the project rests on Emma Stone's shoulders. She is a fine actress, particularly adept with comedy, but as Mia she is a mediocre singer and a subpar dancer. (Note how she keeps looking down at her feet, and how she slouches rather than keeping her line.) One could almost understand this if Chazelle's purpose were a sort of pro-am Everyman musical along the lines of Everyone Says I Love You, but that's pretty clearly not the case.
Also, the music. The songs are trite when they aren't outright unmemorable, and Seb's piano theme just seemed like sad random tinkling. This is a problem, given that Sebastian (Ryan Gosling) has no real personality apart from his love of jazz. There's an awkward pull here between the actual quality on display and the almost art-frat aggression with which the viewer is relentlessly pummeled with the whole Romanticist, never-give-up-on-your-dreams business. The fact that John Legend is positioned as the sellout option here (to say nothing of "I Ran," one of the greatest 80s synth-pop hits this side of Gary Numan) just adds to the sense that something about this world is way out of whack.
It's pretty. Not as pretty as One From the Heart, whose saturated neon aura La La Land superficially resembles. But then Chazelle isn't Coppola, and that's understandable. The 11th-hour bid for poignancy, which actually struck me very much like a Michel Gondry move (let's replay the whole thing in miniature, but with variations -- even cardboard sets!), wasn't a bad touch.
But it only emphasized the real problem at the heart of La La Land. I think we could forgive a lot -- lame songs, bad taste, iffy ideology -- if we actually had any reason to care about Mia or Sebastian. Who the hell were they?