Forget Gaga: Jessie J is who's gonna be keeping Christina Aguilera up at night. Smart, fierce and frank, the British singer-songwriter has pipes would-be divas would kill for -- and the ability to bend them to a wide stylistic range. Who You Are hops from vintage-tinged soul to hip-hop-doused dance-pop to Broadway blues ("Mamma Knows Best"). Jessie squeezes melismatic acrobatics, bold belting and subtler, hushed timbres into each cut without sounding (too) showy. Only the dramatic "Big White Room" feels a bit forced ('til you learn she wrote it as a hospitalized kid).