Luke Thomas’s review published on Letterboxd:
The first two and a half hours of Sergio Leone's epic, detailing the lives of two friends who go from being petty criminals to establishing a criminal empire during prohibition-era America, is some of the best filmmaking I've ever seen in my life. Incredible set pieces, beautiful cinematography with gorgeous wide shots and interesting angles, excellent acting (especially from the younger cast), a beautiful, fairy tale soundtrack and a gripping story.
Unfortunately this is let down somewhat by a turning point in the film that comes before intermission, which makes De Niro's character utterly irredeemable and horribly unlikeable. The final act is also odd and clumsy, with strange, unsatisfactory reveals, horrible aging makeup and lacking in any kind of strong character developments or conclusions. The main character Noodles barely goes through an arc, which is a shame given how well the story is established. In any other film this final act would have been fine, but with it being attached to the incredible first two hours, I was left a little disappointed.
This film excels particularly in the building of tension. Scenes are long and drawn out to build a sickening sense of dread. This is particularly effective in a scene when Noodles is carrying a suitcase of money, with natural sounds being amplified to deafening levels that really makes you sense the characters anxiety. This is also done well in a scene after the intermission where the characters sit silently in the main headquarters, with the simple sound of a teaspoon in a cup being so ominous it will make your heart pound. This use of sound, matched with objects and people often being just out of frame, helps keep you riveted during the entire, imposing run time.
Once upon a time in America is sharp, alluring and beautifully made, which makes it such a shame that the ending couldn't match the dizzying heights of its first two hours. As well as this, the characters don't always feel properly written, and many things are left unanswered or are inconsequential, particularly the female characters which have very little to do. If you can look over these few flaws, then this film is definitely worth watching.