I recommend Hexen! And I will tell you why; it all began long ago, many decades past in a distant world... well, it actually happened here on Earth, specifically in my living room.
Two friends and I were looking for a dark fantasy experience that we could play together, there weren't too many cooperative dark fantasy games back then, but I had journeyed far and wide to the US, and discovered the seductive obsidian gem known as Hexen. My PC was pretty potato back then, so I got it for the Nintendo 64; we turned the game on, each one of us took hold of those spaceship looking N64 controllers, and out story truly began...
All three of us stereotypically fell into our roles. The "strong guy with no brains" in the group took the role of the Warrior, the crafty engineering student took hold of the Wizard, and my ever so saintly (indoctrinated?) self took control of the Cleric. Through fist, wand and mace, we opened our path towards fatal glory. The results were not as expected: the Warrior kept getting stuck in trees, niches, corners and windows, the Wizard kept trying to melee the enemies with his twig-like wand, and I felt my mace was more suitable to mix flour and eggs batter than crushing our enemies' skulls.
But, through perseverance, spending and entire weekend playing non-stop, we managed to obtain powerful weapons and relics, to make up for our lack of competence and skill. Those didn't help with the insanity inducing puzzles of Hexen, that I swear by the gods, we could only complete after I tapped into the force and basically chose the solutions to them through blind guessing; I guess you develop that ability after sleeping only 3 hours a day and having pizza as the only sustenance.
At last, we reached the final stages of the game, and after many grueling hours of getting our hides handed to us by the Heresiarch and Korax, we managed to conquer the game! Just to be greeted by one of those ambiguous endings that many of the Heretic and Hexen fans are all too familiar with.
Those days were truly magical. As we moved through dark temples, swamps and graveyards, with the sound of leaves rustling, the chilly night air, and all sorts of demons, gargoyles and undead trying to rip us to pieces, we felt truly alive as no other time in our gaming careers; it was like reality and fiction had mereged into a single experience. I can remember the first time a swamp monster came out of the murky waters, clawing at my face, as if it had only happened yesterday. I wish with all my soul that the valiant people that pick this game up (available here in GOG for everyone to enjoy!), will manage to re-live that magic; even if they only have a small fraction of the fun we had back then, playing as a small team of doomed but determined adventurers, I'm sure it will become one of your most treasured gaming memories.