Dark Souls II the sequel, an action-packed RPG with an even more open world takes place over much larger terrain - twice as large. The hardcore, punishing difficulty that's the mark of the series will return, with the devs disavowing the "easy mode" gameplay of today.
Dark Souls challenged even the most hardcore players with its emphasis on difficult gameplay. Expect better graphics, more advanced, reactive AI, and a new story to unravel. The plot is mysterious, with the game's protagonist dealing some form of connection to the first game, though this is not a direct sequel.