A lot of people give the 1993 version of Prince of Persia credit for being a mercilessly hard game. For the record, I beat it a few times. The game wasn't challenging, it was just punishing. Stupidly, horribly, punishing. I certainly wouldn't let a game waste my time like that these days. Each individual challenge in the game is fairly straightforward, but there is no tolerance for human error. If you can pull off the individual jumps with 95% accuracy and if a level has (say) thirty do-or-die jumps, then your chances of making it through the level are an abyssmal 16%. (This is based on a simulation I just ran in PHP. There might be a little numeric slop in there because this is working off of a short run of pseudo-random numbers, but this is still more analysis than some designers seem to put into their game. In any case, you get the idea.) With these numbers, you'll have to play every level about five times, which means you'll spend the majority of the game repeating the same content again and again.
I'm actually offended by obvious and gratuitous punishment in games. This can be something like stingy checkpoint-based saves, or a lingering death animation before you're allowed to re-load the game. I'm playing the game to have fun and be entertained, and if making a mistake means the game is going to refuse to entertain me for a couple of minutes, then the game is no longer doing its job. I can understand making me repeat the challenge I just failed. That's proper, and, in fact, I want another crack at that. But I don't want to spend a few minutes repeating the piss-easy challenges that came before, and I don't want to watch a little animation I've seen a dozen times already. The game should only throw me as far back as it's required to allow me to re-examine the situation and try a different approach or figure out what I did wrong. Anything more than that is just padding out your gameplay length at my expense.
There's a reason people talk about games having a difficulty "curve." There is an expectation that a game should ramp up the challenge as you go. It shouldn't be a bland monotonous grind of the same thing, and it shouldn't have crazy unexpected spikes. Prince of Persia: Sands of Time is on my short list of favorite games, but one of the things it gets wrong is the combat. It ramps up the difficulty by just throwing more guys at you with bigger health bars. It's not harder, just more time consuming.
Difficulty, if you'll pardon the expression, is hard. Here's to the game designers who take the time to get it right.