I wouldn't recommend reading this book if you haven't read Sir Arthur Conan Doyle's Sherlock stories...and I'm not sure I would recommend it if you had. To read this, you need an understanding of the cases but also to remember: it's not 'canon'. It's written by a third party and while it is supposed to add to the understanding of Sherlock Holmes' great nemesis Professor James Moriarty, it's not an understanding that's given by Doyle as he wanted to portray the character. A lot of other characters get caught up in this too and I would have thought they are being misrepresented.
Some of the little tantrums Moriarty has because of Holmes are giggle inducing but this collection of papers and things from Moriarty's desk is not well laid out or convincing the way the original Sherlock stories are. The font used, meant to represent handwriting, is also at times hard to read at times and that seems to me to defeat the purpose.