The most promising artist in hip-hop was born in Compton, Calif., in 1987, around the same time as gangsta rap. His first major-label album is as elegiac as it is celebratory — an authoritative memoir of a lifetime spent immersed in the music that has changed the lives of everyone around him, for better and worse. Lamar has absorbed so much from every major MC you can name that he is able to evoke any era or region of rap within a few seconds of his delivery, and his words can resonate powerfully: in “Good Kid,” he calls out gang members who “step on my neck and get blood on your Nike checks.”