When ABBA's sixth studio album was released on April 23, 1979, it was an immediate success, shooting to the upper regions of the charts all over the planet.  The album had been a long time coming, with sessions starting a year earlier, but it was well worth the wait.  Presenting ABBA's trademark mix of songs with different characteristics and temperatures, the group's main lead vocalists, Agnetha and Frida, sang their way through the album with passion and energy, expertly interpreting the music and lyrics painstakingly worked out by Bj'rn and Benny.  It was, in other words, classic ABBA.