It turned Kendrick Lamar into a star.
Kendrick Lamar was big, and the buzz was real, one year ago. But at this point, his singles hadn't really had too big of an impact on radio ("Swimming Pools" wouldn't peak until after the album came out). He was selling out larger and larger venues; I watched him perform in the 3,500 capacity Congress Theater in Chicago in September, 2012, to a packed house.
But he needed something to put him over the edge, and good Kid, m.A.A.d. City was just that release. One year later, and he's guesting on songs by artists like Robin Thicke, and in direct competition with the genre's best selling rapper, Drake. good Kid enabled Kendrick to release "Control," to call out virtually every rapper in his lane. It was the moment that transformed an unlikely introvert into one of the genre's biggest success stories, at a time with true hip-hop stars—on the Drake, Nicki Minaj, Macklemore level—are few and far between. (In fact, he was only the fourth new rap artist—alongside those three—to go platinum since 2006.)