Fallout 3 lead designer Emil Pagliarulo posted a reply to a Fallout fan's question in the Bethesda Game Studio Forums to clarify what players can do in the several viewpoints used in Fallout 3:
"I meant, in general, the game is fully playable in third person. You can run around, adventure, get into combat ('run and gun') etc. all in third person, and the camera was designed to accommodate that kind of gameplay, unlike the third-person camera in Oblivion, which was more of a 'vanity mode.'"
Read his full reply at the official forum.