Half Life 2: The first second I stepped out of the building to see the city at the beginning of the game. My Jaw dropped to the floor.
Half life 2: The moment I grabbed a saw blade using the gravity gun, thrusted it through 2 zombies and cut them in half. Oh my goodness
KOTOR:
Spoiler: The moment I realized that I was Darth Malak's master, and that I have lost my memory
TLJ: The moment I step into the fantasy world of Arcadia