I finished dark souls 2 a few weeks back and am currently in the middle of demon's souls. Can't really notice the differences. Or do you mean dark souls 1? I played 4-5 hours of that too.
Dark Souls I. Haven't played DeS.
Like I mentioned earlier, the game mechanics seem slightly less fair. If I get hit in DaS, I know it's because I screwed up. Not always the case in DaSII. Enemies seem to be aggroed in larger numbers regardless of what you do, small ones to bigger ones, stacking the odds against you. While some people may love that kind of challenge, it seems like a cheap way of upping the difficulty. I've not played enough yet to know whether I'd agree with all the criticisms, but I can see why some people think that the first one is better.
Just so that we're clear, I'm loving DSII, and this is mainly nitpicking. The difficulty of the first, at least in the beginning, will always have been greater to those of us who played that first, without having played DeS, seeing as you're in the dark about so many things, and you've not encountered a game so unforgiving when it comes to your approach to fighting, so I don't expect to be too frustrated by the issues that make this a harder game, like the loss of max HP with each kill.