Roger Ebert wrote:
The Longest Day is not a "classic." It's a hokey Hollywood war movie. John Wayne is ridiculous and too old. The song is stupid. Pre-James Bond Sean Connery is pretty good, but Paul Anka? What the hell? And even when I was a kid I knew they didn't attack Omaha Beach with Douglas Skyraiders.
The book the movie is based on, however, by Cornelius Ryan, is terrific and well worth reading. It's vastly better than the movie. His book "A Bridge Too Far" is also very good and much better than the movie they made based on it (which also has Sean Connery in it).
It is a classic of the now outdated Hollywood co-production full of international stars. In this day and age, you could never get that collection of old and young Hollywood/international stars and pop singers that Zanuck got for TLD. It would be like getting Russell Crowe, George Clooney, Brad PItt, Ryan Gosling, Justin Timberlake maybe even Bieber all in the same picture. Can't happen nowadays. It employed three credited directors for the British/American/German segments, also something that could never happen now. The Hollywood conventions of the day look hokey now, but certainly there are parts that still hold up the like the long helicopter shot of the French paratroopers invading the village. Saving Private Ryan is very good, but add 35 years and it's very likely only the action sequences will hold up, not the sentimental central story and especially the too-good-to-be-real Tom Hanks character.