Katy Perry's Teenage Dream album was largely written by MM, I'd say it's both one of the most important pop records of the last decade and MM's best work. It smashed all sorts of chart records, in total it had 8 top-three singles on the Billboard Hot 100, and 5 number one singles.

It's absolutely destined to be a classic album in every sense of the word, and I find it funny that most music heads I know can't see that because (imho) they are too afraid of being seen as someone who enjoys Katy Perry. Oh well, the kids who were 12 at the time will grow up appreciating it. I suppose it's for them anyway.