Seeing the Work Station Menu's for the first time.
(Having a history with all previous Fallouts, then experience) jumping off a rooftop in Power Armor wielding a minigun, to fight a Deathclaw during a nuclear thunderstorm, only 1 hour into the game.
I sometimes reload the savegame of standing on the roof of Fort Hagen (at night!), when the BoS Prydwen Airship flies into the Wasteland.
Entering the Glowing Sea for the first time
The sight of a spotless clean Institute during the elevator ride down.
Staring 10 minutes straight at the production process of synths in the Institute Robotics lab.
What are the moments that made you smile?