Didn't start the Gangsta era, that was back with N.W.A. It did however revolutionize gangsta rap with its melodic, three dimensional beats. Before that a repetitive loop was used for a beat. Released in 1992 by Dr. Dre following his breakup with N.W.A.
Shit, playin' The Chronic just makes me wanna go to da hood and pump my hydrolics.