I've been listening again to Top 40 recently (I was a huge Top 40 fan in my teens, circa early 1990's and haven't listened to it much since then). It definitely seems like there's a new aesthetic in pop (see https://musicfans.stackexchange.com/questions/3286/is-drake-music) and while it doesn't match my own tastes, as a student of music, I'm interested in its character. What defines the Top 40 sound of the mid 2010's?
Some of my hypotheses:
Intensely personal, idiosyncratic lyrics --a move away from generic and/or universal themes, often with self-empowerment themes.
Rhythmically and melodically complex lines based on natural speech rather than on memorable melodies --showing a strong hip-hop influence across all genres.
Unselfconscious, direct "naive" lyrics --a move away from both irony and symbolism.
A sound with strong retro elements from both 60s/70s pop and 80s/90s pop.
On the positive side, I appreciate how much more interesting the lyrics are now than just a few years ago. On the negative side it all seems very forgettable to me --although maybe that's just a reflection of how many years of pop it's competing for mental real estate against.
EDIT: Here is the current Billboard Top 40 Chart: http://www.billboard.com/charts/pop-songs