A Google Play Music update v5.2 just popped up in the Play Store, though it's being slowly rolled out, as is the case with many big Google apps nowadays. The previous version is 5.1, and indeed I'm seeing quite a few changes inside that would warrant a point release.
Update 9/10/13 4:00pm PT: the official changelog has been posted:
* All Access Genre Radio is here! Go to Radio or Explore, pick your favorite genre and enjoy unlimited radio based on the music you love.
* New download queue that allows pausing, resuming and cancelling
A detailed teardown may be coming in the future, but in the meantime, there is one big change that was immediately apparent: Google Play Music now supports Genre Radio in addition to the regular artist/song radio.Read More