JFK
You thought Oppenheimer had the best cameos and supporting performances? Think again. Pesci, Candy, Bacon, Tommy Lee Jones, Sutherland, D'Onofrio, Rifkin, Oldman, Rooker, etc. Heat check after heat check after heat check.
Thanks to immaculate editing, cinematography, and paranoid storytelling a 3+ hour run time has never felt so engaging and riveting.