I love cranking up an old pc and playing DOS based stuff like Command&Conquer, Shadow Warrior and a game called 'Crusader no Regret'.
The thing about some of these games is the content of some of them - if they were released today, would cause an uproar of complaining...... especially Shadow Warrior.
I also play Conflict Freespace (1 and 2) which are, i suppose, technically speaking flying-type games but they are so immersive and have in my opinion not been beaten!