There's better I say about SUM beyond that it is an amazing, thought provoking piece of work which draws on both spirituality and metaphysics (with a dash of religion, too) to comprise it's work.
What we have here is 40 very short stories, each relating a conceptual idea of Heaven or another form of afterlife. They're not all perfect, some of these are better than others, some really make you think, while others not so much. Its a little hit or miss, but the larger majority are pretty interesting and fun to read.
In one we find that god has abandoned Heaven for unknown reasons, the angels live like homeless people, and everyone is at war not over whether he exists or not, but about the exact nature of his absence. In another the story explains that the afterlife gives you a choice to be anything you want to be in your next life; with a drastic catch.
My favorite is the one where people in the afterlife have to watch all humanity until their name is spoken for the very last time and they are forgotten completely. Or maybe its the one where god attempts to design the perfect Heaven for everyone and weeps because everyone agrees it's Hell.
You could read these stories back to back and be done with the entire thing in a couple hours. It's a short ebook (I'm not even sure if there is a print version) only 110 pages long in my Kindle app. But to really enjoy it you should take your time with it and savor each story. All 40 stories are very short, it takes 2 to 3 minutes to read one, less if your a speedy reader. This makes it perfect for those moments when you only have a few minutes. A quick break at work or lunch is just about right to digest a couple of them. I highly recommend the book.