Dark's souls is its predecessor perfected. Its massive, atmospheric, unforgiving..meticulously crafted by true artists.
The world is absolutely fascinating, a vision entirely recreated from the mind of From Software. It is seamless, never does the style or artistry disagree. Each world is so different, each instilling its own sense of horror, whimsy, and curiosity. You explore, you die, you learn. The game conditions you to succeed. Make a certain move and the game punishes you, gradually you learn through trial and error, classic operant conditioning.
The gameplay remains much the same, but added is much more in terms of depth and sheer content. The amount of content does so much more than simply provide more hours of gameplay and more equipment to toy with. In Dark Souls, the effects of more content trickle down having a significant effect on each feature. Theres many more spells, pyromancy, armor, weapons, and concept that the game takes time to sink into. But once it has settled you'll be hesitant to leave its world, even if to be haunted by it's difficulty.
Dark Souls, is better than Demons Souls. I can't find myself ever going back to Demons Souls only because I'd feel like I'd be moving backwards. Dark Souls perfects the gameplay and combat from Demons Souls and lets you use it in a seamless world broken into segments. The entire world is a landmark in Level design, I have yet to see a game that can even compare to it.
Dark Souls is great, a Demons Souls fan fantasy. An engrossing experience that I will never forget and should be experienced by all for an appreciation of Video games or the arts.