Chaos Strikes Back

This game, and its predecessor, "Dungeon Master" were remarkable games. They fit on a single floppy disk (before 'high density' was invented) and could be played very nicely on a machine with only 512K bytes of memory.

The monsters, setting, and puzzles made it one of the best games of its type.
Ever. Games like "Eye of the Beholder" attempted to duplicate the effort but came up short, in my opinion.