LoZ:OoT - I already loved Zelda and my N64, that game had me gawking at so many different things. I still think its the most amazing game ever made. It is so clever, so perfect. I dont think any game like that will ever be duplicated or equaled.
The most recent was FFX. I dont have the time to play it, I wish I did, but the little amount I got through had me amazed. Nobuo Uematsu (sp? I think thats a good guess
) is amazing, his music is amazing. It still doesnt bring the holy shit factor up to what I saw in LoZ:OoT.
almost forgot...Everquest. The sheer magnitude of it amazed me for two years. I loved the game, but I got burned out after so long playing it.