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