Nethack separates the men from the boys. If you can make it past the 15th level you're officially a gaming demi-god. And if, somehow, against all odds you manage to actually beat the game rumor has it you transcend your mortal coils and become one with the universe. True story!
But yes obviously I've played Nethack. Quite a bit actually. And the difficulty of the game is part of the charm, you aren't really *meant* to win. This is a game built akin to the old style where it was the ride that counted, not fancy graphics or a snazzy epilogue. You do your best, have fun doing it, and try to get a sweet high score. It is also insanely big after having been tweaked and adjusted over nearly twenty years.
For example I was once playing a Monk, worshiper of the good gods and a beacon of righteousness in the dark. Unfortunately being righteous and awesome doesn't mean food magically appears from nowhere, so I was doing my usual thing scavenging food from my fallen foes and buying rations when a shop showed up. Regardless I had just finished clearing my way through some Dwarven mines and one of the Dwarves had been carrying a collection of tinned food, which I was munching on as I descended deeper into the labyrith. About 2 levels lower it struck, my character passed out and was left helpless, laying on the ground doing what I thought was dying from some poison or another as I desperately tried to figure out what had happened! A trap somewhere? A spell? Hunger? I didn't know, and to make it even stranger there came a rumbling as the anger of the good god came upon me for betraying him, and I didn't even know what I'd done.
Then he awoke, and I realized what'd happened and burst out laughing. The food from earlier, one it em had contained wolves mean. *WEREWOLF* meat apparently. And my lawful good monk had been afflicted and transformed into one of the creatures of evil, pissing off the gods but giving my character a whole slew of powerful abilities and making him insanely powerful for his level. A monk werewolf? Crazy good... not good enough however as directed by the wrath of his god all the forces of evil turned at once and began hunting my poor character. I ran, but found myself in a dead end, and there I made my final stand. Howling to terrify my enemies I blockaded the doorway and forced them to come at me one by one, the bodies piling up before me and my Monk leveling at least three times from the non-stop combat.
Then came the Liches, driven from the depths of the deeper levels two of them began to raise around me the dead of my fallen enemies. It was a brutal brawl, fighting my way through the reanimated corpses and trying to get to the liches who stood in the back and continued to bring them to life anew. I got one, it went down swiftly to fang and claw, butt exhaustion set in and my monk collapsed, transforming back into a human just as the hordes surged once again. Fought as best I could, but it was no use. He died. My highest score yet!
You don't get that sorta experience in any other game. I love Nethack. And that was only one character, I've had dozens more. Never beaten the game. Farthest I've gotten was the 18th floor. But you don't *need* to win to enjoy it!