While playing, you'll have two forms. Your primary form is your body form. Once you die, you respawn in soul form. While in soul form, your HP is halved (or if you get a certain ring, reduced to 75% of max) and you can only regain body form by killing a boss or using a certain item.

There are 5 different worlds, with 3 to 5 sections each. It may not sound like much, but believe me it's good enough. You'll be dying enough to make those sections last a good while. Also, each world has a "tendency". It's basically your average yin-yang type deal. Do good things in the world, and it will shift towards white. In white tendency, there are certain events that happen. Enemies will be easier, however they won't give as many souls as they would in neutral tendency. However, do bad things such as killing NPCs and the tendency shifts towards black. Demons will become harder, your soul form HP will be further reduced, and so on. Oh yeah, getting killed while in body form pushes the tendency towards black.