Even if you aren't a musical addict, or an old Abba fan, you'll be overcome with the utter enjoyment this gorgeous cast exhibits as they constantly surprise you (and possibly themselves).
Need another reason? The Greek Isles have never looked so magical without a lot of Disney help nad maybe some cartoonishness.
Musically, the talent is so impressive even Pierce Brosnan (who obviously doesn't need to display any talent at all) should be proud - actually he may actually have been the most pleasant male surprise. Meryl, of course, sang beautifully but most of her fans know she had lots of vocal training, so watch her to experience total abandon right in front of your face (this lady has balls!)
There really isn't any wasted film, sound or moment whatsoever - and no possible excuse not to go enjoy yourself with this movie.