It's really difficult without being overly frustrating, IMO. It definitely does stuff to be challenging, but doesn't go overboard to the point where it feels unfair.

Take dying. You resurrect back at a bonfire, so that's a pretty standard checkpoint. You lose your souls (the currency/XP in the game), which sounds awful, but you don't lose any stats or gear you spent them on, and if you can just reach the spot you died you get them back. Tough, but fair.

And occasionally they'll throw some bullshit at you that will kill you if you're not already familiar with it, which is momentarily frustrating. But, now that you know it's there, you can reliably avoid it, or at least know what to try to do. And that kind of thing doesn't happen so often that you're just memorizing sequences, or have to play the game at a snail's pace to make any progress.

Plus the combat system is just plain great. Frankly I wish more fantasy games were like it, even if they weren't as difficult.

Some people will definitely dislike it because of the difficulty, but the people who like it definitely think it deftly walks the line of "tough but fair." I hate frustration platformers, but I dig Dark Souls.