The review by Vaughan up above is absolutely first class and just wanted to endorse his claims. There are so many hidden gems within these 9 albums and this would probably make a fine welcome Christmas present for an Abba family member or musical friend.
In particular, the bonus 17 track CD is worth getting with a couple of Swedish song versions, plus Elaine and Happy Hawaii highlights. So many of these wonderful tracks tracks are not on the Mamma Mia movie. The Day Before You Came, One of Us, Me and I, Like An Angel Passing Through My Room, Soldiers, My Love My Life, Head Over Heals, Kisses Of Fire, I've Been Waiting For You and When All Is Said And Done make up my top ten ABBA.
A glass in hand, good music and Dance while the music still goes on, over the holiday season and beyond, what could be better.