I thought Dark Souls was pretty hard. I kept playing until I reached Ornstein and Smough* (or however their names are spelled). Then I gave up. Months later, I made a new character, reached them again, gave up.
A year or more later, same yet again. This time I steamrolled everything up to that fight, then struggled a bit with it, then beat it! ...but then I got bored with the game shortly after and didn't make it out of the Duke's Archives
Played DS2 a year later after that and found it extremely frustrating. After wrestling some times with some dude with a shield (The Pursuer, I think?) I just threw in the towel.
Mostly played the Dark Souls games out of a sense of obligation, as completely insane as that sounds. My friends wouldn't stop raving about them, so I wanted to be a part of it, I guess. NOT my cup of tea. No thanks. Moving on.
*not to mention that the way up until that fight was really hard on my blood pressure. My first time through Sen's Fortress was probably the least enjoyable several hours and days of gaming I've ever experienced. It was really easy the 3rd time through though.