I feel like Demon Souls was more about memorization, remember the enemy about to attack you from behind the door, remember the archer shooting you in the back, etc. Dark Souls is more about pure survival. Atleast so far it requires you to just power through.
Bought the game today, played like 3 hours so far and yes, this is true. At first I didn't believe when I heard this in a podcast last week and... well, I'm kinda speechless really. The game is awesome but the focus on surviving is pretty hardcore and yesterday I finished again Demon's Souls and Dark Souls is just pure brutality in your face in comparison.
Hell, I can say that Demon's Souls was a big tutorial for Dark Souls.
Oh also, the animations are longer I can see myself dying a ton of times because my character is still busy attacking when instead I want to stop that bit of animation to heal or defend. I'm loving the gestures though. :)