You seen Platoon? Both my granddad's served in Vietnam. While my paternal grandfather never talks about it, my mother's dad is adamant about his hate of the military, this war, and that one. And he said that's the most realistic one he's seen. It's deep, dark, and depressing. It's gritty... It's just a hell of a movie.
Charlie Sheen (ironically enough) is the main character. Willem Dafoe is in it. Tom Berenger (one of the Wisemen from Training Day) is in it. Keith David is in it. As is Forest Whitaker. It's one of those big-name movies from before they were big names.
Oliver Stone directed it and it's said to be based on his experiences.
lol. You've probably seen it, though... but perhaps all I've said will make someone else see it.