Xbox has confirmed that Fable's main story will be around 15 to 20 hours long, exactly in keeping with the first three entries in the venerable RPG series. You can double that playtime with sidequests and exploration, and the real devotees can play "forever" if they want to treat the game as a life sim.
"We have around 15-20 hours of mainline quest gameplay, we have around 15-20 of side and open-world exploration content gameplay," associate game director Will Kennedy says at a Gamescom Q&A session, via Polygon. "And then, of course, the life systems are limitless, so you can play them for as long as you want."