After installing Windows 8 on my main computer, I wanted to figure out whether my games at Steam would still be playable. I really like the idea of my games being administered from within one application to avoid all the fuss related to registration keys, disk that need to be inserted, updates, even store your progress/savegames. Naturally a lot of companies want to offer this kind of services. Same situation for software, music, movies, e-mail, calendar and online storage of course. I really dislike the way some companies are "forcing" us to use their solutions, and I wish it would be easier to migrate data between different service providers.

Anyway, I downloaded the client, inserted my credentials and synced it with my backed up game storage. Most of my games still worked fine, all except Fallout 3. The plash screen popped up with all the settings and when I pushed the play button it returned to windows. The steam page says officially that "Fallout 3 is not optimized for Windows 7" and I find that a bit old since it worked perfectly when using Windows 7. One explanation I've seen is that it has poor multi core support (more than 2 CPU cores), although that did not stop my old setup from running it (same machine).

First I tried adding the "suspicious" dll file mentioned at this answer to this question, added the changes to the Fallout_default.ini file. It did not work.

I removed the dll and changed back to the original configuration. The next tip i came across was that the Windows gaming center had to be installed and logged into for the game to work. Windows 8 has this integrated gaming center, but the application of interest is found on xbox.com. I logged in with my account, and also installed the K-lite codec pack. I put back two configuration lines in

\steam\steamapps\common\fallout 3 goty\Fallout_default.ini

[General]
...
bUseThreadedAI=1 (change to 1)
...
iNumHWThreads=2
...

Suddenly the game started. I don't know exactly what triggered it, but I suspect the codec pack being important in combination with the configuration. I'm not quite sure about the gaming center, but I guess it does not hurt to have it installed. I can start the game without it running. Next I had to restore my save games located in

C:\Users\<username>\Documents\My Games\Fallout3\Saves