Demon's Souls was frequently frustrating to the point of my wanting to quit, but as I hung on long enough to understand the mechanics under play, I was able to enjoy the novelty and fun of many of its mechanics, and appreciate the excellent presentation of game convention interpreted into a world full of grim realism, buoyed by interesting gameplay, audio, art, and technology. It really is the full package, though it would be difficult to blame anyone for not having the patience and time to experience it.
As a game designer, I wonder whether the absence of information did Demon's Souls any favors. The lack of information was the biggest hindrance to my enjoyment, and though I can see how not understanding the consequences of its world could mimic reality and even bring a community together, that community is diminished for latecomers (me), and game conventions could probably have been explained without breaking context. Even explaining the idea behind not sharing information might have been enough.
Upon completing the game, I was unsurprised by the wave of relief that washed over me -- not an inappropriate feeling after playing the role of a small hero standing up against the forces of an all-powerful demon -- but confused by my urge to play it again on its harder difficulty. It was as if I had finally taken down a most horrible opponent, and while still grasping the hilt of the knife I struggled to kill it with, exhausted, angry, and still overwhelmed with frustration, I had to beat it once more just to twist it.