Planescape is a setting for TSR's AD&D game. Black Isle/Interplay chose this setting for their next CRPG because, frankly, it's awesome. At least, it is in my opinion.

What's so great about Planescape? Well, the first thing is that it unites all other AD&D worlds. It doesn't define a world, or even a universe, it defines a multiverse. This multiverse consists of planes, which can be looked upon as universes. One of these is the Prime Material Plane, the plane where TSR's other AD&D worlds are (with the exception of Ravenloft). Planescape mainly deals with other planes, however.

Here's a short overview of them:

The Inner Planes. These planes are also called the elemental planes, because they consist of the elements, like the Plane of Earth or the Plane of Fire.

The Outer Planes. These planes reflect moral, psychological elements rather than physical elements. Good and evil, law and chaos. In the middle are the Outlands, a neutral plane. When on the outlands, the closer one is to a certain outer plane, the more the Outlands start to resemble that plane. In the middle of it all is the city of Sigil, a city shaped like a ring, floating an infinite distance above the Outlands.

The Astral Plane. A silvery void that connects the outer planes with the prime material plane. Don't let its nothingness fool you; this place is dangerous. The Githyanki make this place their home. Another notable feature of the Astral Plane is that there are corpses of gods here... Some are used by the Githyanki as floating fortresses.

The Ethereal Plane. This grey fog connects the inner planes to the prime material plane. It's a bit more peaceful than the Astral Plane, but it still has its dangers. Like demi-planes. These were created by powerful wizards as "pet-planes". These wizards, as a rule, don't like to be disturbed.

The city of Sigil merits some special attention. Not just because it's shaped like a ring, but because it's seen as the center of the Multiverse. It is 100% neutral ground, enforced by a being known as The Lady of Pain, or just The Lady. This being has incredible power. She has the power to keep the gods out of Sigil (which she does) or to imprison any individual that is threatening to endanger the neutral character of Sigil. It has portals to virtually every single plane.

Ok, so there's a lot of cool places in Planescape. This is not what's important, however. The most important thing about Planescape is belief. The planes are shaped by belief. The people living in a certain place can change it (and even move it to another plane). Not surprisingly, various philosophies have united in so-called factions.

Torment. Pain that defies description. What greater torment imaginable than to be devoid of identity and not to know one's place in this endless stream of madness we like to call The Multiverse?

This is exactly the dilemma you face in Planescape:Torment, Black Isle's upcoming masterpiece. You are The Nameless One, a lost soul in a crazy world. You're immortal. Every time you die, the same thing happens: you just wake up again. It's a day like any other in Sigil, the tire-shaped city seen as the Center of the Multiverse by many. And you wake up, looking just like another corpse in the morgue, complete with scars. You, however, have a bit more life in you than usual for the residents of this place, and you decide to get up. Who are you? How did you get here? You don't know, but you're determined to find out.

So we've got an interesting storyline with a cool main character. For the modern gamer, these aren't enough to make a good game. The modern gamer wants gameplay. The modern gamer wants graphics. The info that's currently available about the game suggests the game will have these things.

You've probably heard of Baldur's Gate, Interplay's previous AD&D masterpiece. Baldur's Gate revived the CRPG genre by combining awesome graphics, a good story and addictive gameplay that allowed for real-time combat while remaining true to the AD&D system and allowing intricate strategy through use of the pause function. Just in case you stopped reading after the first part of last sentence, let me summarize: Baldur's Gate rocked.

Torment will be using the same game engine, called the Infinity engine. This means awesome graphics. Torment will also use the same real time battle system that Baldur's Gate used. This means: Gameplay. And then some.

If you're really interested, here's a list of features.

Torment is about discovering the identity of the Nameless One, through various quests. A feature that reflects this is the system of character advancement. Since you're immortal and you've been around for 10,000 years or so, you don't need experience to advance in power. You just need to remember stuff. How does this work? I don't really know, but I imagine it would go something like this: In one of your past careers, you were a priest of a certain god. Now, you just happen to witness some sort of ritual honoring that god and BOOM! you remember some of your clerical powers.

Also, the game refines the "alignment" system. (a system in AD&D describing a person's moral perspective: law or chaos, good or evil) Instead of a permanent alignment (as in Baldur's Gate: you choose an alignment and it never changes), Torment features a dynamic alignment: your alignment is changed according to your actions. Also, NPC alignment is more subtle. When a character joins your party (5 NPC's can be in your party at any given time), his/her alignment isn't immediately apparent. It will be later, when the character acts according to his alignment. Speaking of NPC's: they're very alive in this game. Party members will interact even more, and will affect the game more.