As far as I'm concerned, I love a game that challenges me. One of my all-time favorite games is Super Meat Boy, a game famous for its rage-inducing difficulty curve. And I'm quite good at it at that. For me, the harder a game is the better. Few modern games provide a genuine challenge to me, either the difficulty is dumbed down to appeal to the least common denominator, or the difficulty just results from bad design, bugs, etc rather than genuine difficulty, while games like Super Meat Boy and I Wanna Be The Guy are genuinely challenging, to the point of Angry German Kid rage. Which is precisely how I like it.