The game that got the most traction with me was Skyrim. I played it through for the first time in the early days with the game in a vanilla state. I have since finished it 3 more times with various mods and playing with different builds. Fully modded, Skyrim can be turned into one of the most visually stunning games ever created.
Total Annihilation, it is a strategy unlike anything ever created resources are static but dynamic at the same time. Some of the guys at Uber are working on expanding on the original game.
Loom and many other Lucas Arts or Sierra adventures. But Loom was truly amazing, it was beautiful, had an innovative game mechanic and wonderful music. I remember always watching my father play it, and after that I had to get into gaming as well.
I always find myself replaying the Baldur's Gate series... And each time, it always feels fresh to me. Sure hope Pillars of Eternity can emulate the experience.