Planescape does have some minor tweaks to the engine from the one in Baldur's Gate, but the setting is the main aspect which sets itself apart from its predecessor. Planescape is a whole different world than the one that Baldur's Gate was set in. The focal point of the action in Planescape is the city of Sigil, which represents the center of all planes, or dimensions in this universe. Supposedly the whole town of Sigil is filled with portals that will allow you to warp to any point in any universe. The catch is that these portals will only open for the right key, which could be anything - a physical item, a song, or even a string of thoughts.
Some portal entrances are more obvious than others.
Fact Planescape is expected to take at least 3 CDs. Maybe they'll also offer a DVD edition like Baldur's Gate. Inc. All Rights Reserved.