Let's not get carried away. "Apocalypse Now" was Martin Sheen's only real "mega-movie." Most of his career was in made for TV tripe (he made a career of playing JFK.)
My favorite movie of his is "The Final Countdown" (1980.)
My favorite movie with him in it is The Execution of Private Slovik. He gets blown away at the end.
Sort of like why I like Mission to Mars....Tim Robbins blows up in his space suit. Great stuff.
“The story of Eddie Slovik, who was executed by the Army in 1945, the only American soldier to be executed for desertion since the Civil War.”