Nothing of the last three generations. Console RPG's usually have sporadic difficulty, a hard section or area, or boss. Most of the time you can just back track and grind your way to victory. This game is far more challenging than even SMT games on hard mode, and is beyond any FPS or hack-and-slash title I can think of. Granted I haven't played every single game, so I'm sure people can think of balls hard games that might compare.
One thing that makes it tricky is that grinding is very hard in Demon's Souls because of the risk of losing all your souls from an accidental death. Even if you spend hours boosting stats, the difference is relatively small since you are boosting one stat one point at a time, and each successive boost costs more than the previous. It gets expensive after a while and the law of diminishing returns kicks in. Grinding is kind of good after you beat the first boss. I recommend grinding enough to get some basic magic and upgraded weapons, but character advancement overall is really incremental.
The best analogy is really Contra or Ninja Gaiden on NES. You only beat those games without cheat codes in one of two ways: Get really good, or memorize every scenario by rote and through grueling trial and error you might win. Demon's Souls is like that.