Here are two great war movies, on opposite sides of the spectrum. The first one is a great "movie" movie. You know, a great time at the movies! The second one is a war movie will sink you into freakin' hell, possibly make you feel ill at times it's so disturbing (and it achieves this with very little gore effects!).

As already mentioned by FanFiltration, "Kelly's Heroes". All star (big!) cast, great writing, great location shooting and costumes and sets, great action... It's funny, exciting, tense, at times it will practically make you cheer...! Even the music is awesome! This flick has it all! Really, if you've never seen it, you must! This is what having fun at the movies is all about! :)

And on the other end of the "war movie" spectrum is "Come and see" (a USSR movie, original title "Idi i smotri".) I'm one of those people who really didn't like Saving Private Ryan. I give Dale Dye a huge amount of credit but all the contrivances, the bad writing, the overwrought John Williams score in that flick... >:P
A few years later "Come and See" was at a local theater, and seeing it I couldn't believe that this film was made in '85! (I really suspect that Spielberg saw this before making SPR; there's one thing in SPR that had "never been seen" in war movies before, but it's here in CAS 13 years earlier!) Truly ahead of its time. I don't want to pump it up too much as some people say it's overrated. (but I'll still take a jab at such people and say they're out of their mind.) It's not a fast-moving film, not full of great characters who you'd like to be your pals if you were plopped into a crisis. It's just a slice of one of the most terrible (surrealishly so) times in human existence (and this is not a prison camp movie). Alright, shutting up now on it. :)

To throw one more out there, one not seen too often: "Stalingrad" (1993) Not quite a great masterpiece of a film due largely to its veering off from what the subject matter should supposedly offer (the battle of Stalingrad!), but pretty darned good, very worth a look for the harrowing atmosphere, epic scale/scope of the production, and the brutal/realistic graphicness on display in the battles and such. Probably goes without saying, but don't watch the dubbed version.

When you have time to watch something beyond movie length, the HBO mini "Band of Brothers" mini is excellent, highly recommended! (this coming from someone who basically hated SPR!) It's the highest rated thing (that has over a few thousand votes) I've ever seen on IMDb: rated 9.6 out of 10! :O I've watched all ten hours twice now.

That's my two cents. ;)