Another really tough year.
Dune 2 started RTS, Wolfenstein 3D started FPS. And I have great personal nostalgia for both.
Indiana Jones and the Fate of Atlantis is arguably best Lucas adventure on gameplay, if not as funny or atmospheric as some others.
Shining Force is one of my top 20 series.
Defenders of Oasis is a wonderful little Game Gear RPG.
King's Quest VI is perhaps my favorite of the series.
I'm voting Ultima Underworld. I only played it couple years ago and was pleasantly surprised. I'm not a big fan of westerns RPGs, Baldur's Gate or KotOR won't get my vote. But I really enjoyed UU, it was so much ahead of its time and remains a highly playable and entertaining game even by modern standards.