I recently played an amazing DOS game where you have your country and you can declare war or peace with other ones, and i really enjoyed it. Growing up one of my favorite DOS games was Gobliiins 3, such cool memories!
Duke Nukem 3D, absolutely no question whatsoever. The first game I played that had environments that aped real life and had real life levels of interaction detail... Light switches, CCTV cameras, so much incidental detail and environmental transformation. No other game had done that to the same extent before then and I'd argue that no other game has done it since!
My parents refused to spend any sort of money on videogaming so my childhood was spent scrounging for anything I could on my Dad’s 386 PC. Shareware of the first episodes of games was a Godsend, I must have played through the first part of Duke Nukem 50 times.