Had an issue where the game would stutter when looking in a specific direction. It was unplayable.
Changing bUseWaterShader from =1 to =0 in the Fallout3.ini file in your documents/my games/fallout 3 folder fixes this issue.
Topic on Talk:Fallout 3
After changing "bUseWaterShader" setting, must then use an alternate game launcher, such as the Fallout Mod Manager, to launch the game or the setting will be reset.