It's a mix of a casebook "created by John Watson" and brief sections on various aspects of the show, Holmes' mythology, and how each episode relates to the Doyle version.
The sections written by John have post-it notes from John, Sherlock and occasionally Mycroft. The font used for John and Mycroft's writing was fine, but the font used for Sherlock doesn't look right to me at all. I'm not sure what font it is but it just doesn't fit. It seems too neat and print like. Part of me thinks he'd use elegant cursive and not care if other people could read it or not, but he's so fastidious about grammar that I think he'd want his writing to be legible so he could communicate clearly. I want to see that sign from Scandal in Belgravia to compare the writing.
The casebook also contains a few pages on 221B, though it's mostly the living room and kitchen.
Some of the post-it note conversations are pretty amusing. Sherlock makes fun of John having a casebook at all (of course). He has apparently arranged John's ties by dominant color theme and is quite annoyed with the suggestion that John might arrange his own ties.
Where John describes his date in The Blind Banker Sherlock has a post-it note calling it the Best. Date. Ever. and when he talks about the subsequent kidnapping Sherlock's note is 2nd. Best. Date. Ever.
When talking about the apartment we get a few titles that Sherlock's reading as well as a tall stack of My Weekly which Sherlock apparently reads, but of course that doesn't track with not knowing who Connie Prince was.
I enjoyed it, and if you like the show you should check it out.