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