What exactly is Google Play?
Google play is not the renamed version of Android Market. Instead, it brings all the services that Google offer to android devices onto a single platform. Everything, right from you log in credentials to market the interface everything is just the same. But, Android market will be replaced/renamed as Google Play. Google has also started rolling out the update for the same.
Whats new in Google Play?
Google cloud is a service which allows you to access all you stuff form anywhere be it reading a Google Book, listening to music, renting a movie everything is in the cloud. In one sentence you can watch read listen to your favorite from anywhere you want.
Read more about Google Play:
About Google Play