I love Leone, but I wasn't taken by Once Upon a Time in America. However, I also just kind of caught it part-way in on cable. However however, I also first encountered The Godfather that way, and it was mesmerizing. The Godfather is easily one of the greatest films ever made. Godfather II is terrific, but I don't quite get people who think it's better than the first.
I'll note that there are a handful of fan commentaries for Godfather, Godfather II, Wizard of Oz, and Casablanca, but zero commentaries for Citizen Kane. It's slow, methodical, character-based, and narratively complex but emotionally simple. It's ingeniously shot, and as a result is mainly beloved by directors and cinematographers, not film lovers. Wells and most reviewers prefer The Magnificent Ambersons. I like much of Wells' other work better.
In short, if DIF does it, very tough to do well.
Now, Apocalypse Now also has zero commentaries, and is nearly the opposite of Kane. It's methodical but not slow, episode-based, and narratively simple but emotionally complex. Plus, it has explosions and helicopters and other crazy shit.
In short, that's a win-win, regardless of your opinion of it.