Wizardry IV: The Return of Werdna
Wizardry IV is hard as nails. You play the evil protagonist Werdna and start at the bottom of a ten level dungeon. Climbing back and regaining your powers along the way are the goal of the game.
It's not so much about character development and grinding like the other Wizardries.
The game challenges you with riddles, teleports, dark areas, pits, chutes, rotating floors and random instant kills. You have to fight parties of the first 3 Wizardry games that players have sent to Sir-Tech.
You have to explore and map carefully to have any chance at all. You need a lot of patience to beat this game. You get no experience points for surviving battles. You only regain power by finding pentagrams. You can summon monsters for your party and regain health and mana at the pentagrams, too.
Don't play this, if you never played a Wizardry game before.