Terrible.
I have a Google Home and Chromecast audio, and getting Google Music to interact with the two in any reasonable fashion is nothing short of a mess. This is crucial to get right, but Google has failed, and failed to fix the issue. Google Home by itself works great. Getting Google Music to use Google Home as a whole home speaker is a flaming pile of software.
With Alexa coming out with a similar system, Google better get their act together.
zboyl709 about
Google Play Music, v3.35.1010