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