
Now mind you, game difficulty is a different beast for me these days. I'm a level designer and more and more mainstream games are less geared toward making the player actually figure anything out for themselves more than greasing the skids.
It's a mark of professional pride--I make levels, I make the puzzles in reverse order too, and I'll be damned if there's someone else out there setting out puzzles (outside of Jonathan Blow) that's going to stump me for any length of time. But have the past few years of soft-pedaled difficulty in games dulled my skills?
Knowing the typical workflow of setting out challenges for players doesn't always aid me as a player. Playing all the Hitman games didn't set me up for what I was getting into with DTS, and neither did the game itself.

Sure, the tutorial/intro gives you a mechanical understanding of 47's capabilities, but not the rules of the game world or what to expect from the mission proper. And so Anathema starts you with perched on a hillside overlook of an Italian villa, with a priest to rescue and a man to kill and damned if you had the faintest idea of how to go about it.
Which in some respects is a pity--once you know the rules of Hitman games the missions become sublime; you can finish them the first time through with a Silent Assassin rating (given for surgical prowess) without prior knowledge of the mission simply because all missions are constructed with certain unwritten rules in mind.
On the other hand--isn't the genius of Super Mario Brothers that the elegant simplicity hides the depth of play? Trading tips with friends, secrets? Remember riding home from a trip to the store with the game box in your lap, pouring over the manual for every kernel of information about the game you were about to play?
If through trial and error you bested Anathema and gone on to even greater challenges, later you could return to that first mission and find it all laid out before you, clear as day.

I feel a little lost, but I also feel as though I'm being treated like an adult; a welcome change after the tutorializing excess of several recent AAA titles. I happen upon the F1 key, which actually does give me a pretty good overview of individual mechanics, even if it doesn't give me a thread to string them together.
I am cautious, I save and reload and restart the mission with a different approach, intent on gaining this game's equivalent of Silent Assassin rating--but this game follows the travails of a Russian SMERSH agent, do they care about bodycounts so long as the job gets done?
About an hour or so in on my first tentative mission of a surprisingly difficult game, I hesitate.

Now that's the deep end. I know I probably wouldn't be looking back on the game fondly at all without the steady stream of reliable strategems and real-time advisory from siblings also having played or currently playing X-COM--but the truth of the matter is that I do look back fondly, much as a whole generation of children, regardless of their predilection for gaming now look back fondly on trading tips and mastery of Super Mario Brothers. (Except not at all; those kids were clearly too stupid to save the Earth from an insidious alien threat.)
I still haven't made much headway in Death to Spies but it's a welcome return--a return to the days where developers assume the player can think and can deal with consequences on all by themselves. That I can appreciate.
What games do you admire despite/because of their difficult learning curve?