Eh, it's alright but nothing special. The thing is, it covers a wide scope of areas, but because it does this it's inferior with regards to the detail it goes into. It has sections on game theory - Sklansky's books are better at dealing with this. It has sections on psychology - Zen and the Art of Poker and (from what I hear) Psychology of Poker are better at dealing with this. It has a tournament section - the HoH books are better... etcetera etcetera.
I found the most interesting part of the book by far to be the early sections detailing Greenstein's past, to be honest.
You will probably get more out of it if you haven't read a lot of poker literature previously, though.