Fallout 3 has received a new update from Bethesda years after launch on Steam, and this is not a minor bug fix.
The update removes the requirement for Games for Windows live from Steam, which was causing many crashes and required workarounds.
The issue was not present in other store versions like GOG.com.
For fans of modded games, Fallout 3 script extender is now no longer working due to the update, and it might be some time before it is fixed.