It's just that it has a realistic approach to combat. Most players aren't used to it, since there are no other games with that approach (as far as I know). It took me a couple days to realize I'd just not be able to play the game if I didn't focus and actually take combat seriously.

Another thing that increase the games fame of being hard is because it doesn't treat you like you mother like newer games do. Kinda like “Oh, is it too hard for you son? Choose easy.” and “Oh you died? No problem, I saved the game 10 seconds earlier, just try again.”. Demon's Souls is more like: “You either take me seriously, or go play something else.”

Bottom line, after getting used to it, it gets kinda easy actually.

The paths on the level are somewhat easy-ish, and you'll pretty much only die because of traps and stuff. And for whatever reason, while a few Bronze bosses are extremely difficult to deal with (giving the early impression that the game is very hard), most of the the Silver bosses are total pushovers (and let's not talk about the final boss). Overall, once you gain some levels, you'll progress very quickly.

This is the best nex gen game I've yet played.