The title of her second album, My Everything, perfectly sums up the content: she tries so many genres. This might make it feel a little disjointed, but one thing is consistent - her voice is stellar, akin to a young Mariah Carey.
The relatively slower songs truly allow her voice to shine: on Just a Little Bit of Your Heart it's uber-sweet yet soaring. (However, the song's about loving someone who two-timed you. Ouch. Bonus fact: 1D's Harry Styles wrote it!)
It's a shame the ballads aren't as well know as Problem, Break Free and Bang Bang. Then again, those songs are so catchy, we can't blame them for hogging the spotlight, or the featured artists - Iggy Azalea, Jessie J, Nicki Minaj, the list goes on - who helped push the songs to the top of the charts.
But trying to put "everything" in one album results in too many styles, and not enough substance.