Dungeon Master, an epic 879 KB game from 1987
en.wikipedia.org
en.wikipedia.org
I even tried getting some of the modern remakes and fan-based sequels, which were many megabytes and had fancy graphics and sounds. They all paled in comparison and were simply not playable. This 1987 game is a testament to solid games not needing any fancy graphics, just brilliant game design that is deep, challenging, and interesting.
I highly recommend playing it, you can download it on the internet easily and it runs on DosBOX.