I would love love love to be able to fight Isshin the Sword Saint from Sekiro: Shadows Die Twice.
When I finally beat that pole weaving old man it was a great gaming experience, and I've been into gaming for a long long time now. A close second would be when I first beat Half-Life 2. That game really amazed me. Had a major impact on me moving into tech too bc I got so into the modding scene.