Assuming by "beating it" you mean the main quest, I can tell you the main quest is only a tiny part of Fallout 3. The best parts of the game have nothing to do with the main quest:
the Tenpenny Tower quest
helping Reilly's Rangers
Point Lookout
The Pitt
watching a Mr. Handy as he recites a poem
retrieving Vengeance
stumbling into the Plunger Room of Death
finding all of the Gnome vs. Teddy wars
fighting through a horde of Level 30 enemies to get to the Burnmaster flamer
The Door
mezzfriending the entirety of Evergreen Mills
helping Bryan Wilks move to a new home
I've spent over 2000 hours in Fallout 3 and still haven't seen and done everything.