Absolute Sandman 4 contains issues #57-75. It is dominated by The Kindly Ones, and The Wake. The book as a whole is very focused on Dream, and you can see the mechanisms turning from the first few chapters, once you know what to look for, drawing the book to a very interesting showdown. Spoilers ahead, so proceed at own risk.
What I liked most about this book was that it was the story of a Dream, but not necessarily the Dream. It really is a story about stories, and it makes sense that Dream is most closely followed throughout the series, because Dreams are, in effect, stories that parts of our brains tell to other parts of our brains.
I also really enjoyed that the end of the book and the end of the series evoked very similar emotions, and they amped each other up really well. The end of the series was regretful but optimistic, in a way, and it definitely made you look forward to a new story that, while it wouldn't be Sandman, might be as evocative as Sandman. Different stories not being worse than each other has come across as sort of a theme that I've picked up from Neil Gaiman's vast array of characters, too. There are many different types of character, and many different stories within the framework of Sandman, and it's never implied that any of them are, at their essence, any more desirable or worthy than any other. Which I like.
People who know me will no doubt already know of my dislike for endless character-saving deux ex machina, and my liking to see that major characters aren't safe just by virtue of their necessity to the story. So I very much enjoyed the ending. It made me very sad, being that Dream is nearly my favourite character, but I enjoyed the thought that it was just one aspect of the essential concept of Dream that died, and not the idea itself. And I enjoyed seeing them farewell him in such a fitting manner. I haven't started the fifth volume of Sandman yet, but it will be very interesting to see what it adds to the main body of the series.