The lowest common denominator has indeed struck game difficulty to the low-end of the spectrum. The fact that people put limiters to their own gameplay (I shall not use any potions, I shall not wear any armour and shall use only non-damaging spells....) tells something about the difficulty of those games. In my consideration, if a fully priced game is over in less than 30 hours, it was too easy. And if it got over that 30h limit just because you're forced to grind etc then it was a bit poorly designed. Really, how many players these days hate Nethack, because it doesn't reward them instantly here and now the first time they play it?
Do you remember the golden times with Commoder 64 when you might wait for half an hour for a game to just load from a casette? After that, you didn't stop playing after 5 minutes unless you had to. You pushed forwards, you overcame the obstacles and when you finally beat the game despite the complexity curve (after tens of hours of gaming) you could go out and say 'I did it!', feeling like you were on top of the world.
Where is that feeling these days? It's hiding behind strategy guides, cheat codes, trainer programs, difficulty curve that might make a five-year-old stop for 10 minutes before beating it and the ultra-realistic graphics that make you watch in awe for a minute and then leaves you wondering 'This was the game? Why didn't I buy a photoalbum?'
That's why I love Galactic Civilizations 2: The AI playes by the exact same rules as you do (it doesn't cheat) and if you crank the difficulty up you will get totally pwned within the first 20 minutes. Unless, of course, you're pretty damn awesome yourself.
Challenges are fun. If I want to have fun without challenges, I'll go watch a movie or buy a book instead of playing a game. Really, those a cheaper, they last about as long as apoor game and you don't feel like someone cheated you out of your money if you don't like them.