I may be in the minority here, but I prefer 2008's unruly One of The Boys to its genre-obedient successor. That earlier album came from a rockier place and married a mischievous spirit - rather than MTV-sanctioned shock for shock's sake - to a gum-snapping sense of empowerment.
The latter has always been Perry's strongest lyrical card, from I Kissed A Girl through Firework to recent hit Roar. But with only the mild bhangra flavours of Legendary Lovers to keep Roar in interesting company, Prism becomes a disappointing parade of over-the-top power ballads and calculated dancefloor bangers. Walking On Air imagines Madonna doing 1990s house; Ghost allows its mature face to be stomped on by big production beats.
Perry's personality breaks the surface from time to time, but there's too much external control on show here.