RDR ending
Vice City, when Lance betrays you.
Vice City again when i realized the game had cinematic missions with a structured story and wasn't just random violence (first GTA ever played in 05)
When i finally learned the Street Fighter commands
MGS4 when the game goes back to shadow moses, the nostalgia, the feels
Finally beating Missions that took me weeks to beat in SA, which then led to even harder missions that took me months and then YEARS.
FINALLY BEAT the game in 2011-12 if i remember correctly.
playing GTA IV for the first time was just

in itself