Tales of the Sword Coast was released as the expansion.
Nobody thought it could be better until Baldur's Gate 2: Shadows of Amn came out in 2000. Gameplay was even better, story just kept getting better, and the best part was everybody knew an expansion was coming.
Finally The expansion to SoA came out entitled Throne of Bhaal. It is the final installment of the series. Beating the game gives you a combination of incredible accomplishment and also terrible depression from the realization that never again will you experience an RPG like it. Now we must all make do playing it over again and fantasizing about it while playing Dragon Age.
Baldur's Gate is the perfection that all other RPG's are measured against. And they all fall short. Dragon Age came close, but only close.