Full list of all 72 Fallout 3 achievements worth 1,550 gamerscore. It takes around 60-80 hours to unlock all of the achievements in the base game on Xbox 360.
The base game contains 50 achievements worth 1,000 Gamerscore, and there are 5 DLC packs containing 22 achievements worth 550 Gamerscore.
Took the G.O.A.T.
Completed "Take it Back!"
Completed "Agatha's Song"
Completed "Reilly's Rangers"
Reached Level 8 with Bad Karma
Reached Level 14 with Bad Karma
Reached Level 14 with Neutral Karma
Reached Level 14 with Good Karma
Killed 300 creatures
Picked 50 locks
Collected 20 Vault-Tec Bobbleheads
Collected 10 Vault-Tec Bobbleheads
Reached Level 8 with Good Karma
Won 50 Speech Challenges
Completed "Trouble on the Homefront"
Completed "Oasis"
Made one of every custom weapon
Discovered 100 locations
Completed "The Nuka-Cola Challenge"
Hacked 50 terminals
Killed 300 people
Kill all the Super Mutant Behemoths
Completed "The American Dream"
Completed "Finding the Garden of Eden"
Completed "Picking up the Trail"
Completed "Rescue from Paradise"
Completed "Strictly Business"
Completed "The Waters of Life"
Completed "Head of State"
Completed "You Gotta Shoot 'Em in the Head"
Completed "Tranquility Lane"
Completed "Scientific Pursuits"
Reached Level 20 with Good Karma
Reached Level 20 with Neutral Karma
Reached Level 20 with Bad Karma
Completed "The Superhuman Gambit"
Completed "Those!"
Completed "Galaxy News Radio"
Completed "Following in His Footsteps"
Completed "Tenpenny Tower"
Completed "Stealing Independence"
Completed "Blood Ties"
Completed "Big Trouble in Big Town"
Completed "The Wasteland Survival Guide"
Reached Level 8 with Neutral Karma
Completed "The Replicated Man"
Completed "The Power of the Atom"
Placed a grenade or mine while pickpocketing
Completed "Escape!"
Got the Pip-Boy 3000
Completed "Operation: Anchorage"
Completed "Paving the Way"
Completed "The Guns of Anchorage"
Completed "Aiding the Outcasts"
Completed "Free Labor"
Completed "Unsafe Working Conditions"
Found All 100 Steel Ingots
Completed "Into The Pitt"
Reached Level 30 with Good Karma
Reached Level 30 with Neutral Karma
Reached Level 30 with Bad Karma
Completed "Who Dares Wins"
Completed "Shock Value"
Completed "Death From Above"
Discovered all locations within Point Lookout
Completed "A Meeting of the Minds"
Completed "Walking With Spirits"
Completed "The Local Flavor"
Completed "Not of This World"
Completed "Among the Stars"
Completed "This Galaxy Ain't Big Enough…"
Collected all Alien Captive Recordings