For the 25th anniversary he's going to go back and tell the story of what happened to lead to the whole saga. Sandman started with Morpheus trapped by Burgess (who'd tried to summon and capture Death), and it's mentioned in Brief Lives that he was returning from another galaxy, weakened...and now we get to find out what was going on in that other galaxy. Prequel! Whee!
I hope Morpheus is still all 80s though, and not drawn in his Absolute style. Since when has he had rippling muscles