Mental Floss has their list of The 25 Greatest War Movies of All-Time. There's a number of films on the list that I haven't seen like their #2 choice La Grande Illusion (1937), Twelve O'Clock High (1949) and The Battle of Algiers (1966). I'd also disagree with a lot of their rankings (MASH doesn't hold up for me) but to each their own. And how does Paths of Glory (1957) not even make the list?
Vulture also has their list of The 50 Best War Movies Ever Made. I'd also highly disagree with their rankings. All Quiet on the Western Front (1930) ranked 20th? That's crap. That movie should be in the top 5 on any list easily. And by Vulture's reasoning The Outlaw Josey Wales (1976) should qualify but is not on the list though it's much better than some of their picks. Same goes for the movie 300 (2006).
How does The Battle of Midway (1942) or Tora Tora Tora (1970) not make either list? Seems like an anti-Navy bias.
I did my own Top 5 List of the best war movies over a decade ago. I would have to heavily revise my list today. May do that sometime soon but not until after I've seen 1917.
As an aside one movie I've had on my list to see because it came highly recommended in a couple books is John Huston's The Battle of San Pietro. The movie didn't make any of the lists (probably because it's categorized as a documentary) but I thought it worthy of mention.