One of the best old school PC RPG/Dungeon Crawls
This came out post Dungeon Master (I played this series on my Amiga). Used the same first person "grid style" movement scenario and was very similar to that game.
I had a blast playing this on PC when it first came out, was a ton of fun. Not sure how well it would hold up today with great modern titles in this style of game like the Legend of Grimrock series and Might and Magic X (same style though turn based). I'm giving it 5 stars simply out of nostalgia and the fact that it was fantastic when it came out on PC.
I never had a chance to play part II and III, I heard 2 was just as good and 3 was by a different team and not as well received.