About 20+ years ago, playing Zork I. There was a scene that you fight some monster with a knife but unlike any other adventure game I played to that point, the outcome of the battle was not fixed but actually determined at runtime. I was simply amazed. That moment made me later play through all Zork and most other Infocom games.
The other moment was about over 6 years ago when I first set foot in Vesper, Ultima Online. It took me several moments to realize that I was inside a living and breathing fantasy world and that the other avatars around me are being controlled by actual people somewhere on the other side of the world. That moment was awesome and the next couple of days playing UO were unlike anything else I experiences in computer gaming.
- barvaz