There are personal stories about DeNiro, but as the author notes, DeNiro is a private person that doesn't like giving interviews so it's hard to get a real feel for who he is.
I found this to be a very detailed book on DeNiro's film career.
It gives the background to each of his movies, his preparation for the role, how the movie was reviewed and how successful it was. Also, original cast choices, for example, on Silver Linings Playbook, Bradley Cooper and Jennifer Lawrence got the roles, but originally they had Vince Vaughn and Zooey Deschanel in mind and then Mark Wahlburg and Angelina Jolie, but they backed out.
Also, Schindler's List was a Martin Scorcese movie that they let Spielberg have so they could make Cape Fear instead.
"You talking to me" was taken from Bruce Springstein concert.
And there was an insinuation in the book that John Belushi who was DeNiro's friend OD'd on heroin because he was trying to be like Deniro in his extreme method acting and took the drug to prepare for a character he wanted to portray in a movie.
I do agree his movies haven't been to the same standards as his early work, but I can't expect him to throw himself into the roles like when he was young and single with a family.