i think games should be marginally hard.
today you can see the downward curve of learning and toughness of games. say CoD for example.
every time i see a new one, i see less recoil, better "perks", less balance etc... it makes the game too easy,
but also ruins experience for some in multiplayer.
on the other hand you have games like dark souls - tough but rewarding games. and i think games should be like that. not maybe that tough though, but they should be tough and rewarding.