Unlike his famous Dollar Trilogy (The Good, the Bad and the Ugly etc.), Sergio Leone's Once Upon a Time in America is not a western film... but swap the New York streets for a desert landscape, and you could argue it kind of is.
It has a reaaaally long running time. Initially Leone wanted to make two 3h films, then he made it it a single 4h29 film, that distributors got him to trim down to 3h49. It was released in the U.S. as an R-rated 2h19 film that made little sense (too many scenes cut, and rearranged into chronological order as if American audiences couldn't understand non-chronological narratives) and that Leone dismissed as "not his own film". Today people are trying to restore Leone's 4h29 original. In the meantime I saw the 3h49 version.
I liked it a lot, its running time actually plays in its favor because the director has time to ease you into organized-crime-era New York and into the plot (you just need a long evening ahead of you). It kind of made me think of 2019 The Irishman which, surprise, also has Robert de Niro and lasts "only" 3h29. The non-chronological structure is great, don't know why anyone ever thought "this would be better if we put it back in the right order", this is not a history lesson. And Ennio Morricone's score is fantastic, although I think I preferred his scores for the Dollar Trilogy (which felt more creative and more expansive, this was more similar to the Cinema Paradiso score, beautiful theme but not great as a score, it's single vs album, if this makes any sense, but now I'm listening to the soundtrack again and I'm not sure I agree with the previous statement anymore).