The last quest of the main quest was extremely lazy, the final "boss" is able to be killed with a single shot (you dont even have to fight him if you use speech) and the ending was just there to quickly round up the game.
Fallout 3 is a terrible Fallout game, a bad RPG and a ok Action-Adventure game which is what it should be seen as, a Action game with minor RPG elements played to pass the time.