At the turn of the last century, contemporary R&B entered a second adolescence. The power ballads of the 1990s were fading out, replaced by crossover hits that pushed the limits of the genre by incorporating dance, electro, and hip-hop into visions of a glittering future. The 28-year-old singer George Riley was born as this cultural transition kicked off—and her new mixtape, the shiny, upbeat, slightly irreverent More Is More, makes a close study of early ’00s pop.