Doom is my favorite old game. I remember playing Where in the World is Carman San Diego with my dad. All the Duke Nukem games like Duke3D with plutonium pak (atomic edition), Duke it out in DC, D!ZoneII (with Duke Xtreme), Nuclear Winter, etc. I loved Heretic and Hexen, they both took place in the same universe. I believe Hexen was the first game to be continuous, where there wasn't any levels (like level 1, 2, 3, etc.). It also was the first to have puzzles in a fps where you had to backtrack. Wolf3D (with extra episodes) with SOD.