The different responses to this question are brilliant. Some thoughts I must mention:
TL;DR: I think the best examples of this genre are some of the best games ever made.
I played Bloodbourne first, and it was fucking brutal.
I always considered myself a gamer™, so when I first played BB and got killed by the very first enemy, then transported to a different location with no warning, I thought "what the fuck is this? Poor game design, is what."
But it isn't. The beauty of these games is that the best ones make you feel like death is all but guaranteed and the loss of resources is such a tough thing to recover from when you first start playing, but once you persevere you find that death is barely a penalty at all, and the resources you acquire as you go further into the game more than account for any you may have lost earlier on.
I kept at BB and soon was feeling a kind of thrill and fear about what was lurking behind every corner that I'd never experienced before and it was utterly engrossing. Not only that, but the reward of overcoming a tough encounter was massive.
The feeling of exploration is unparalleled as well, which may be my favourite reason to play. Stumbling across a shortcut, or going down a really obscured path which in any other game would be "out of bounds", only to discover you've unearthed a massive, sprawling environment is one of the greatest design feats a game can accomplish imo.
Last thing I'll mention: I completely understand the hate. Especially for Dark Souls II, where the punishment for death is so high, but that game is actually designed for true masochists, and when I first started playing these games and didn't know about any of their strengths beyond "These games are commonly considered really hard", it was exactly what I was hoping for, and it delivered.