Dungeon Master is an amazing game, even today. I originally had it on the Amiga, and remember it took me months to complete... after playing it again recently though it only took a few days to get through - bad guys just aren't as tough as they used to be.
The sequel Chaos Strikes Back tries to do pretty much the same, but the game is a LOT more difficult.
Later came Dungeon Master 2, which I recently played. It's a decent enough game, with better graphics and sound, but it doesn't feel quite the same as the original.
Anyone into this game must check out this dedicated website -
http://dmweb.free.fr/
It has downloads of all the games, plus all the hints, tips, maps and walkthroughs you could dream of.