When Revan takes off her mask in KoTOR, that was a whoa! holy shit moment.
Also when you confront Baan Teegan in Dragon Age, having him as a relatable patriotic character just sucked all the cliched good vs evil out of the scenario, it just completely changed how i felt about him.
Oh and when i collected every item in Titanic Adventure out of time, but the pearl necklace.
so excited that i had saved the world, prevented hiter's rise, stoped the russian revolution, and saved the Rubayat. Then i get back and find out that the necklace funded the black hand, and led to the Rise of fascism over Europe