You can upload your songs into the cloud library and listen them using web or Android devices, you can upload your personal music collection to a single library, even if it’s scattered across multiple computers. .
Google also said that you will be able to listen songs if you are not online, it means if you are offline you had access to your online music, You can also select the specific albums, artists and playlists you want to have available when you’re not connected.
As per me Google Music will cache the certain number of recently played songs and they will be available to you offline.
Create your own custom playlists with just a few clicks or use Instant Mix to automatically build new playlists of songs from your collection that go great together, Your all playlists will be sync automatically and you don’t have to worry about it.
Google Music also allows you to upload iTunes library and all playlist to it.
Currently Google has not announced the storage space available but we think they will provide plenty of space to you and you will never feel out of space.
Google Music is currently in Beta stage and available via invites to US users.