Since so many people mention skyrim, it's an aweful example of a hard game, because:
higher difficulties just change the damage taken, damage done ratio, with adept being both 100% and master being 50% done and 200% taken. The game mechanics themselves are quite simple since the ai works by a pattern.
Guilty as charged me too, thanks too that one bloody skyrim boss with the hammer, who killed my char (300hp about as much armor) in one hit (or out-of-thin-air finishing move -,-)... must have saved like 8 times on that guy alone.
I would really love to see Skyrim with a difficulty mechanic, which is more like:
damage-done/damage-taken/ai-behaviour
1/1/lenient-learn the game
1.1/1.2/new tactics (by enemy)
1.2/1.4/higher speed or lower reaction time for the player
1.3/1.6/new tactics
and so on...
I like the new xcom on classic ironman though (somewhat 70 restarts until i beat the game, because I was stubbornly trying to use a southamerica-scientist based start x) )
[guilty as charged of alt-f4 in my more recent xcom runs]