Why do we love the games that hate us?   Mark of the Ninja
strikes an impressive balance between challenge and reward, but
it's certainly not the only game in recent memory to do so.
XCOM: Enemy Unknown, Super Meat Boy, Dark Souls (and Demon's
Souls before it)--these are all commonly used as examples of
games that are difficult but fair. We often joke that they're
made for masochists as a result of their extreme challenge. But
difficulty in and of itself isn't all that appealing, and will
yield only frustration if handled poorly.  In a recent interview
with Dark Souls producer Daisuke Uchiyama, he describes
difficulty as a vehicle through which players obtain a sense of
achievement. "We often ask ourselves: Why do people continue to
play, continue to torture themselves, when playing this
difficult game? The underlying concept when we were first
developing [Dark Souls] was not to make a difficult game, but to
provide a sense of achievement, a sense of accomplishment." 
The time I spent playing Dark Souls for