In 1988, SSI's Gold Box series redefined the Western idea of the RPG genre. They took the single most important set of pen-and-paper rules -- Advanced Dungeons & Dragons -- and tied them to an epic series of campaigns that spanned entire continents and several games, breathing life into Gary Galax's legendary creation. Running out of steam in the early 1990s, however, the D&D franchise was left to languish. Until, that is, BioWare created Baldur's Gate. The effect was like stepping through the rainbow, like moving from black-and-white to colour.
Baldur's Gate was teaming with life in a way that no other RPG had ever been. Where the Gold Box games had provided hack-and-slash gaming supported by blocky graphics, Baldur's Gate offered would-be adventurers an abundance of quests and meaningful interactions across huge playing fields;across intricately detailed, beautifully rendered isometric recreations of a completely convincing fantasy medieval world.
The transition between Baldur's Gate and Baldur's Gate II: Shadows of Amn was every bit as pronounced. The sequel may have streamlined the interface, but it bulked out the playing experience. Like the Gold Box games, players could import their characters and items from a previous game, and as those characters grew in power, so the game changed to reflect their newfound influence. Building up their own strongholds and followers, they were free to lead their own way through a labyrinthine plot that weaved together divergent and mutually exclusive subplots and quests -- indeed, some subquests were as weighty and complex as the entire first game.
As far as gaming goes, it's a satisfying complexity that has yet to be eclipsed. Indeed, Baldur's Gate II is probably still the pinnacle of the Western RPG.