Although there are many games that I have liked in different times of my life these are my first loves. They like a first car or first girlfriend, you'll never quite capture the same passion or freedom you felt with another game.
The Elder Scrolls III: Morrowind
Age of Empires 2
Pokemon Red for the original gameboy (good 'ol grey brick)
Shadowgate managed to spawn a life of its own separate from the other titles. Deja Vu, even though it was the original and the only title to get a sequel, pretty much vanished and its sequel did not do so well. Uninvited was probably the least well known although possibly the best written. But Shadowgate managed to get a following, was recreated on several platforms and even had some non-Macventure sequels made on platforms like the Nintendo 64.
Shadowgate, the original, was just several weeks ago released as a completely reinvented title that is available on GOG.
Adventure Games. I find First Person Shooters an extension of Adventures, especially if it isn't all shooting and there are stories and skills needed, like Half-Life and ALIEN: Isolation.
Currently playing ALIEN: Isolation and Kentucky Route Zero...