Dark soul's really isn't as hard as people make it up to be.
It can be quite unforgiving if you venture too far unprepared but after a few hours when you're used to it each segment in the game compares to a puzzlegame, where you try the same thing over and over until you get it right.
You also lose your souls if you die (which essentially is both your currency and xp) but you can mostly easily pick it up before you die again (if you die again its permanentely lost).
Also there are a few reaaally easy way to grind souls, and even a soul glitch that gives you infinite souls so you can run through the story without much trouble.
It is an awesome game however and yes it is challenging. It's just that there's so many ways around the difficult parts if you really want to dumb it down, I can't exactly call it "hard".
Newgame+ (after you completed it the first time) can be much harder though because then the monsters will level with you, so you can't grind your way to faceroll-mode.
Personally I think what most people considers hard in dark souls, is that when you get completely facerolled by a new enemy type, a hard area or a hard boss; it sometimes feels utterly impossible, that nobody can make it, and so people give up. Just keep trying and you'll cross that barrier, until you reach another area that feels even harder until you figure it out :)
Edit: I think the atmosphere in the game has a lot to do with that feeling of being hopeless sometimes. They did it really well in that regard ;) After a 10 hour playsession you can feel quite mentaly unstable lol.