TOD
My mom and dad probably watched some of the old ones on TV when I was a kid, but Patton was my first one to watch on purpose, and at a theater. I was sort of dragged to it by a friend who was a little older than me, who had always felt a strong connection to his dad's participation in the war in Germany. Well, I ended up liking it -- the acting (it was my introduction to George C. Scott and very likely Karl Malden), the music, the scope, the color.
Interestingly (to me), it played its first run in the same fabulous suburban Cleveland theater where we saw Lawrence of Arabia in re-release for the first time in roughly that same year...followed by The Godfather which was my first time experiencing actual lines at a movie theater.
But I digress!
Patton
M*A*S*H
Full Metal Jacket
Platoon
And in more recent times, Dunkirk in 70mm IMAX
Although not a war movie aficionado as such, I'm sure I'm leaving out a few that I've really liked. I've also had Paths of Glory sitting here in a to-be-watched stack for the longest time.