Dislcaimer: I work at Google but not on this team. And I'm a Sonos owner, so I think my feedback is relatively unbiased. I got a demo of two of these in my friend's house the other day. The sound quality is exceptional. In a stereo pair the sound was loud and clear throughout the range with good bass as well. Very impressed, plus it's just a nice looking device imo.
Sure there are quirks but the ability to control Chromecast is great, and also the audio is impressive for listening to Podcasts such as DotNetRocks from my phone.
I hooked the bundled Chromecast Audio to the Line In on my Asus Sonar Deluxe 1.3 HDAV on the HTPC, which connects to a 20 year old Rotel Preamp + Amp combo (separation of concerns!), and equally old (but since then refurbished) Infinity Kappa speakers. Sound quality is great that way, so I didn't see the need for a Home or the Home Max which I knew was coming.
So I can say stuff like. "Hey Google, play {some album, artist or playlist} on the PC", and it'll cast to that if I want the big sound. It is way easier than navigating Spotify on my phone or using the Spotify software on the HTPC itself (which is limited to 1 account, with the hassle of logging out / in).
I wish Google could publish server software for Win10 so that I could cast to that as a Chromecast target rather than go via the Chromecast Audio. However I understand there's probably DRM reasons why efforts for this to happen were shut down.
As a PS, my 7 year old son absolutely loves talking to Google. It's pretty impressive to hear him figure her out.