It depends what you apreciate in a war movie:
Honor, heroism, the real suffering or special effects ( because there are people who watch movies only for this ) or else.....
You name it........
I say : a good war movie is the one which makes you fear it.
Good war movies: The Pianist ( Excelent movie)
Schindler's List
Enemy at the Gates. Very acurrate retelling of the Battle of Stanlingrad(the Russians used suicide waves often in the early part of the war). Band of Brothers was very good, also read the book. The Omaha beach assult in "The Longest Day" is just horrendous. See Saving Private Ryan for a more accurate look.