http://www.pcgamer.com/monster-hunter-worlds-story-campaign-will-last-40-50-hours/

The Monster Hunter series is poised to make its western PC debut with Monster Hunter: World next year, which is something Steven and Austin seem pretty pleased about. Last week, we learned that Capcom plans to add new beasts over time via free updates, and now it appears its core story campaign will last somewhere in the vicinity of 40-50 hours. 

Speaking to German publication Mein-MMO.de (via Gematsu, translated by Google), Monster Hunter: World's director Yuya Tokuda suggests 40-50 hours is about right for the game's story mode, however this will ultimately depend on the individual player's approach.