The GFWL issue with "Fallout 3 Broken Steel", the most recent DLC from Bethesda, has been fixed and the game is now available again through Live.
"To access the DLC (Games for Windows and Xbox 360), make sure you have the Fallout 3’s latest title update, version 1.5. When connecting to LIVE, you’ll be prompted for the update. Alternatively, PC players can download it from our site.
Unlike the previous DLCs, The Pitt and Operation: Anchorage, Broken Steel’s questline requires the player to have completed the main quest before venturing on. If you haven’t reached the game’s end, you’ll still notice the game’s new achievements, level cap, perks, enemies, weapons, etc.
We thank you guys for being patient, and we hope you enjoy Broken Steel. To discuss the latest DLC, head to our official game forums."