I have mixed feelings about this product.
The book is too heavy for using it at a gaming table easily. The binding is ok, and I have had no problems with it yet. The quality of the illustrations varies a lot, the quality of the printing in the heavy paperweight version is ok, and the space management and layout of the elements of the book is a bit underwelming.
"Ok" means "sufficient, but not great".
The books gathers a lot of gaming content. It touches the History and metaphisics of Mage, the worlds beyond Earth, and allows for player characters from the Traditions, the Technocracy and the Disparate Alliance factions. It covers a lot of topics but does not move into much depth. Some players claim that certain things are explained in not a deep enough detail for using them in the game despite taking many pages of the book. I am prety sure any compenent Storyteller will manage to make something out of the content even if it is not explained in full detail, though.
The content is badly organized. Certain pieces of information are duplicated, which is a problem because the book is already big as it is. I think it would be hard to follow by a newcomer to Mage: The Ascension.
I think the "focuses" of certain Traditions/Crafts/Conventions are arbitrary and that the authors did not put a lot of thought into making the suggested tools/foci related to the paradigms represented by each faction. Hence you get cybernetics and hypertech as suggested tools for Verbena mages -who are portrayed as druidic mages with primitivistic beliefs and points of view. A good Game Master is obviously going to hack this if need be, but it looks ugly to me.
As a side note, there has been some Internet drama and forum flaming because the authors made an active effort to be socially inclussive towards homosexuals and transexuals, that is, to include characters with gender identity crisis in the fiction and so on. Most of the time it is not annoying and it feels like a natural incussion. Some of the time you feel like they shoehorned a political advertisement at some sidebar. I think they had good intentions but did a lousy job: it is ok to have a computer advertisement in the Linux Magazine; it is ok to have ethics advertisement in a religious magazine; it feels odd to have ethics/political advertisement in high end entertaiment books for which you have paid premium. If they wanted to publish a socially inclusive product, they should have learnt from authors who introduce such concepts in a way that does not feel like the element was placed in the book just because they wanted to do a political declaration. Onyx Path also messed it up pretty badly when addressing related flames in the forums by sutting down, suspending, banning and locking related forum threads and people who disliked the way this was done.
The book is entertaining to read and can be used as a source for inspiration. If my books suddenly burned down, I am not sure I would buy it again, however. Too "average" for a 20th Anniversary edition.