Asadullah Khan’s review published on Letterboxd:
Once Upon a Time... in Hollywood is the newest film by Tarantino set at the end of the 60s in, well, Hollywood. Following Rick Dalton (DiCaprio), a struggling actor, and Clif Booth (Pitt), his stunt double, more than any other Tarantino movie, Once Upon a Time oozes the director's style of letting scenes play out and stay. It's meandering, to the point that there are flashbacks that go on for so long you forget it's a flashback. Pretty much throughout all of the film, you get the feeling as if you're transported back to this time owing to a slick production and veteran direction bringing the old L.A back to life ultimately making it the Tarantino film you can chill and relax with the most. A picture where perhaps simmering in the scenes themselves takes precedence instead of focusing on the plot points/threads and conclusion.
What further adds to that are the solid performances by virtually everyone in the film regardless of how minor the role is. Phenomenal job by both the leads; DiCaprio was energetic and sometimes crazy as usual and Brad Pitt was brimming with coolness, and they sold me on their characters easily.
With that being said, the meandering nature does get tiring at times, whether it's a flashback or simply a scene that you don't care for as much as the previous ones. At almost 3 hours, you do feel the length. Margot Robbie as Sharon Tate felt like she was vastly underutilized. She looked gorgeous but honestly, it felt as if that's all she was there to do and I wish Tarantino somehow wrote her into the climax because when the credits start rolling, there is this certain feeling of unfulfillment, and after watching a long-ass movie, you don't want that.
As an experience, I'm glad and respect Tarantino for putting this out. It was refreshing. But at the same time had some things been tweaked, it would have been a more fulfilling experience for me personally. Still, it's enjoyable, it's hilarious (one of his funniest if not the funniest), I loved the performances, the climax was crazy fun and while I don't think I'll be watching it ever again, I'm glad I had the experience. Give it a watch if you're in the right mindset of a long movie to chill with, especially if you're a Tarantino fan. And if I were to rate it, I'd give it a 7-7.5/10.