Re: Dark Souls!
Dark Souls is harder than Demon's Souls but just in a more frustrating way.
The combat throughout the game is equally difficult. The bosses (at least for me so far) are a bit easier in Dark Souls because you can almost always summon help. But expect to fall. A lot. You will fall off ledges, wooden platforms, cliffs and into water. You will always get cheaply knocked off by enemies.
The only problem I have with Dark Souls so far is that it's basically Demon's Souls version 1.5. Which isn't a big problem since Dark Souls is such an incredibly great overall game. Demon's Souls seems like it was a test run to see "are people actually going to like/buy such a hard game?". When the answer was yes, they decided to fine-tune the formula.
You can tell how similar Blighttown is to the Valley of Defilement (I HATED this place) from Demon's Souls. But you can also the great refinement with no longer having an artificial hub like the nexus. I'm really amazed by how well all the different sections of Dark Souls' world are connected together.