Lead writer for Assassin’s Creed IV says the main story will take about 20 hours to complete

“It’s about, I’d say, 45 minutes total content through the whole story. The main path in the game takes about 20 hours on average. Its actually quite a bit longer than other Assassins’ Creeds have been because the naval stuff gives a very different pace to the game, a very different feeling to the way exploration works.”

– Assassin’s Creed 4: Black Flag lead writer Darby McDevitt