So I'm wondering who this is going to appeal to?
The music store just seems too little, too late. It hasn't got the selection of iTunes and Google decides to release a music store literally a DECADE after Apple unleashed its market-dominating music store.
Most people buy their music from iTunes. That's a fact. It's become the place for the common person to download music (legally). The fact that all of your purchased music, movies, and TV shows can be downloaded to any i-device and any computer at any time is gravy, and the interface can be figured out by anybody. It's built right in--there's nothing new to learn.
If you're more involved in the tech behind your music, you can buy iTunes Match for seven whole pennies per day, and it works through the same iTunes that the average consumer has been using for ten freaking years. Why would the average consumer care to move to move their library to another company and learn a new interface and a new way to redownload load songs?
Add to that the fact that browser-based music stores haven't met with much success (if you have no Internet, or it goes out, or you're traveling, you can't download new songs on your computer or Wifi-only devices), and it leaves a lot open to question.
Now think, not as a tech "insider," but as an average, Joe Six Pack, "can't name the three branches of US government" consumer (aka, the largest consumer group out there), who just wants something cool, easy to use, and familiar, why should I care about Google Music?