Probably playing this game on Christmas day, reaching Megaton and getting lost in that small town. I looked at the enormous game map and got so overwhelmed that I quit playing for about a month. When I finally got back to playing in January, FO3 became one of my favorite games of all time.
If you want an enormous map, check out Morrowind. It is so large that after two or three years my character had only discovered 75% of it. It is huge compared to Oblivion, FO3, and Skyrim.
My favorite memory in Fallout 3 is when me and three companions fast traveled into Takoma Park and landed in the middle of a Talon Merc patrol. Well, they started shooting, and we started shooting, then their robot cut loose with a bunch of rockets. I kind of stood where I landed and was making Fraps movies as my companions did their thing. Then the cars started exploding, and the robot kept blasting with the rockets, so I jumped into the fray, taking out what was left of the robot with four shots of my A3-21 Plasma Rifle. Then after the cars settled down, the girls finished off the last Merc. “I’m down,” he said as he as they finally killed him.