Leave it to Bethesda to give us a game that shuts up all the talk of how games are getting shorter and shorter these days. The average action game is estimated at 6-8 hours. Fallout 3 is looking at 40 hours and side quests. Then again, when has Bethesda ever done the "average" game? Among those 40 hours of gameplay, you will be shaping the opportunity to view one of 200 game endings. That is a lot of endings.
For more on Fallout 3, stay tuned to Gaming Target.
source: Fallout Post Nuclear Blog