The book is somewhat fascinating. But also depressing. Alan Greenspan had the authority to curtail the excesses of the banks which led to this collapse. He gave Congress the incredibly lame excuse that he believed the banks would be more responsible and careful (my paraphrase).
IMO Greenspan has always been the egghead-doosh that he has always seemed.
Regarding the book, I am regularly astonished by Michael Lewis' access to the main characters, from Michael Burry to Billy Beane to Leigh Anne Tuohy (although he's known Sean since childhood). That adds drama to what otherwise would be dry and depressing stories--he's the best contemporary storyteller I know.