Barring some small frustrations, Play Music is arguably one of Google's finest iPhone apps to date. It's fast, smooth as it comes and extremely nice to look at. Using iOS 7 a little more – back gesture in particular – would have been nice though, seeing the iOS 6 style keyboard in November brings on a sad face. The biggest issue isn't even Google's fault, but since you pay for subscriptions via Google Wallet anyway, would an in-app browser perhaps have been a good way to get folks subscribed without having to pay Apple a cut for IAP's?
10,571 App Store customers have shared a review for Google Play Music. Ratings are middle of the road averaging 3.5 out of 5 stars all time. The most current version of the app has 90 ratings with an average 3 out of 5 stars.