This was the moment for me:
The buildup from the first scene riding on Agro, that beautiful OST, going to a distant land that had nothing outside of silence, the mysterious girl, the spooky voice, still confused on why all of this is happening. And then seeing this for the first time on your 32 inch old square TV during the PS2 days. Not only was my mind blown with the sheer size if the Colossus, but this was the moment I took videogames more seriously as a form of art and complex story telling. I have never had a moment like this again.
However, I was fortunate to play Ace Combat 4 and MGS3 right after this masterpiece. Let's just say it was an amazing summer. Literally back to back bliss.
Edit: I have had this moment again:
This opening was literally one of the most beautiful experiences I have ever encountered in a game. And I am not even a huge racing buff.