Demon's Souls is not hard. It is harder than most contemporary titles, but 5 hours into it I am not feeling challenged, intellectually or physically.
What it is is soul-crushingly boring. Combat is plodding and unengaging. My character's moveset is small and shallow. Enemies are diverse, but defeating individuals boils down to memorizing their few near-identical attacks. 90% of combat is spent herding crowds of enemies, or waiting for some armored dipshit to finally swing so I can counterattack. The game hails from the "brown" school of realism and features very little music -- ostensibly to heighten tension, but in reality because what little music there is is embarrassing.
When I die (which is not nearly as often as has been claimed), I feel zero impetus to retrace my steps; not out of frustration, but because they were only marginally entertaining the first time, and don't bear repeating. I have returned to this title over and over, trying to understand all the good things people are saying about it, and I just don't see them. It has terrible gameplay and terrible production values. The poor checkpointing isn't a dealbreaker, but it's one example of a broader lack of effort in the game as a whole, which is really what kills it for me.
I understand the game takes some work to get into, but I feel 5 hours in I should at least see the payoff, and so far it hasn't materialized. I'm not sure how much longer I'm supposed to play before it suddenly becomes deep and engaging, but I just don't have it in me to trudge any further.