Fallout 3 is, somehow, ten years old later this year. Having only played through the Capital Wasteland once myself, such a milestone might prompt a return—and if I do, I might play with kvatchcount's Simply Uncut mod installed.
By my count, Simply Uncut reintroduces 53 NPCs, weapons, armour sets and schematics missing from the full release game. Margaret, for example, is the blase Galaxy News Radio technician that's heard on-air when/if Three Dog dies, but is never actually seen in the game.
Mister Mulberry, on the other hand, is a bespoke Mister Handy found in Megaton; while Officer O'Grady appears in Vault 101 upon the player's return. "It was unknown exactly his original purpose," says kvatchcount of him, "but seeing as he had his own unique police baton, it was deduced he was a stereotypical Irish Officer. Placing him where he is now felt right."
On the weapons front, Simply Uncut adds a unique shotgun named Pa's Fishing Aid, brass knuckles named Love Tap, a bat named Curse Breaker, an American Assault Rifle named Wanda, and loads more. Armour sets include the likes of Pink Power Armor, Chinese Jumpsuits and The Devil's Pigtails.
Full details on all of that and more can be gleaned from Simply Uncut's Nexus page, which is also where you'll find installation instructions. Creator kvatchcount notes the base game's Broken Steel, Mothership Zeta. Operation: Anchorage, Point Lookout DLC are required.