I'll join the bandwagon and say that I have not played a game that I think deserves a 100%, but there are two I consider really close.
The first is Baldur's Gate 2. Everything about it I loved, but the best parts were the characters and writing. I remember getting giddy when a dialogue box would pop up and one of the chars would banter with another, or having my char develop a romance with Aerie, or having all the chars give a little speech to the main antagonist right before the final battle. These things wow'd me more so than any other game has, with only the Mass Effect series collectively coming close.
The second is Persona 3. Same song and dance; I loved the chars, the story, but it was the presentation that really sold me. Everything about that game oozed the running themes of hipness, youth, vigor, excitement and uncertainty. From the music, to the battle animations, to menu screen, this game had more style than anything else I had ever played, and the only game that I think beats it is Persona 4, but I have fonder memories of 3. Persona 3 is the only game I wish I could "forget" so I could go back and re-experience it all over again with fresh eyes.