Great choice! Who can forget Red Buttons hanging from the clock tower, watching his buddies get shot to hell by the Germans? Or Wayne being rolled around on a cart with his hurt foot, being The Duke. Actually, parts of the movie were quite good, with the Buttons episode being one of them, and based on something that really happened. This is a flick that cries out to be made again, with all the CGI special effects we have today. I'd love the see the battleship Texas blasting the beaches. Saving Private Ryan was excellent, although it lost some of it's appeal with repeated viewings, but it was a film that focused on a small part of D-Day, not the grand picture presented in The Longest Day. If anyone wants to see an extremely good and realistic WWII film, rent a DVD of Battle Cry. It's outstanding, and follows a platoon during the Battle of the Bulge. One of my favorites.
Sergeant York with Gary Cooper and Walter Brennan It's actually based on the true story of a WWI hero, but the film came out in 1941, and was designed from the ground up to make Americans enthusiastic about WWII. It's a motivational propaganda film disguised behind a patina of truth. There were many films that were actually worse that came out during WWII, but those were generally so poorly written, and were produced on such cheap wartime budgets, that their lack of realism doesn't stand out among all of the other faults. One example of this would be So Proudly We Hail! with George Reaves and Claudette Colbert. (The best moment of the film, in a morbidly fascinating way, comes when George Reaves' character makes a reference to not wanting to commit suicide. Reaves, of course, was the guy who first played Superman on TV, and died from a self-inflicted gunshot wound.)
Not really a war movie, but just about any James Bond movie would seem to fit your other criteria. I.e. the scene in Goldeneye where Bond breaks out of the Russian military base and then dives to the falling plane to get away.
I would say McHale's Navy starring Tom Arnold was unrealistic. You would have to be the judge on whether it was any good or not. Personally I don't think it was all that good.
How about the Great Escape? It was a great movie, but I think that the GIs were portrayed as being much better off then they were in real life.
Are you looking for a war movie with unrealistic violence or a movie that is unrealistic about the history of WWII? U571 might qualify for both. Pearl Harbor is also pretty unrealistic even if it is violent but I wouldn't call it good. Kelly's Heros would qualify too since its practically a 60's Cannonball Run view of the WWII. I think in terms of unrealistic violence I think almost any war movie prior to the late 70's wouldn't have very realistic violence.