Each album has the original soundtrack as well as lots of great extras such as unused tracks, demos, and alternate versions of songs. They also come with lots of notes and information related to the music on the discs.
My favourites of the collection are the Disneyland and Aristocats collections. The Disneyland one because I love any chance to listen to park music, and this comes with 3 discs full of great pack music including music from Disneyland Park and Disney California Adventure Park. I also really love the Aristocats collection as it has so much great music including one of my favourites "Everybody Wants To Be a Cat", as well as some really fun "Lost Chords" and Bonus Tracks.
You can purchase the albums separately, or as a collection with the box at Disney Music Emporium.
I look forward to seeing what new music they have in store in the near future!