As time rolls on, programmers find new, and innovative ways to keep the player interested for longer periods of times.
i.e. Adding a mega mushroom to *NEW* Super Mario Bros on the DS, or the element of enemies attacking your last known position in a stealth game like Splinter Cell: Conviction.
I think the difficulty of games is more of an age/experience issue. Sure, different games have different play methods, but lots of games have similar mechanics that you could already be used to.
In Spyro 3 on the PS1, I was having the hardest time every beating the Sorcerer on that last level, but now it seems like child’s play.
All game genres have their easy/medium/hard games, no matter what era we’re in. I remember playing Bionic Commando for the NES, and finding it so much harder than the more recent remake. I also played the original Castlevania on the PS1, and found it MUCH easier than the newest ones on DS.
There’s also that difference between challenging, and fucking stupid hard.
An example of challenging would be one of the bosses in Dead Space. Never once in that game did I put that game away because the boss was unfair, or stupid. It’s never fuck you in the ass.
Now, fucking stupid hard would be a game like Ninja Bread Man.
Just, horrible. That game was frustrating. Jumping was terrible, combat was terrible, the camera was game breaking. It just kills me on the inside that they’re making a second one.
All in all, it’s just a matter of what game it is. It’s all very varied, and you can’t give a definitive answer.