From Software is planning to make Dark Souls as difficult as its predecessor, and similar in style. Players still create their own characters, though there are no longer different job classes. There are tweaks to the world design, as well: the world is no longer divided into levels, instead being one large area.
Other players will be able to inhabit that world in some way, in both cooperative and competitive play. According to Siliconera, you'll be able to feel the "gentle presence" of other players through interactions like notes left for other players at the place of death.
Update: 1UP notes that Dark Souls will be published not only in North America, but also in Europe by Namco Bandai Games.