Meeting Sovereign from Mass Effect 1.
So let me get this out of the way. I didn't like KOTOR. I still don't like KOTOR. I had very little allegiance to Bioware. I found the dialogue so utterly tedious that I was talking to bland NPC after bland NPC in the hope that something, anything would trigger a side-quest and I could move on with life. I sit through Metal Gear Solid exposition, I skip through KOTOR exposition and read the text. That's how dry and forgettable it was for me. And the combat left me cold. Same for Dragon Age.
I went into Mass Effect three times, abandoning it after feeling the same Bioware fatigue I felt from KOTOR. OK combat, mainly tedious dialogue. The fourth time, I ploughed on and got to Virmire. I was feeling it more finally, and was in an ok groove. Then the conversation with Sovereign happened. Good lord. There was something about having the rug totally and utterly whipped away from you at that point. Again, the magic combination of placing of the event, the music, the delivery. At first you think it is a simple ship AI, then it dawns on you. Possibly the most spine chilling reveal of a the true antagonist. Kudos for keeping it in full view for the game but not letting on.
Yeah, that papered over the dry side missions and totally changed my perception of the game. The second is the better game, but doesn't have a moment which peaks like that.