I tried Avalon Hill's the Longest Day full Campaign game once. OMG it was a monster with an estimated playing time of 5400 minutes!
http://www.boardgamegeek.com/boardga...he-longest-day
The modular scenarios were more manageable and quite fun to play but I gave up on the full blown campaign after about 30 hours of playing. It was just way too biig to be serisously managable for just 2 players and with more the coordination of who was managing what got very complex as well. Shows what a masterpiece of management the actual campaign really was.