Two steps forward, one step back. This book contains a lot of helpful information for how the magick system of mage works, with one glaring exception, it doesn't expand on the incredibly terse definitions of the different sphere ranks present in the core rulebook. Prime is the worst offender. Although they don't elaborate on the already confusing termonology, such as "Enchant Life" (what does that even mean?), they do seem to arbitrarily add prime as a requirement for lots of effects that previously seemed to not require it. They also bring back some rotes from previous editions of Mage, such as the Prime 2 "Rub Bones" effect that deals bashing. Does it says literally anywhere in the Core Rules that Prime 2 can do bashing? Nope. Does it explain any reasoning behind this exception? Also nope. I ended up making a document to keep track of the various ad-hoc rules changes How Do You Do That introduces into the system. After reading it, I wanted a follow-up book to answer all my outstanding questions. Maybe they can call it "Why Can You Do That?"
You'll also find some effects that suffer from inexplicable sphere bloat and some other strange rules "people who use energy or chi as a paradigm have to spend quintessence per effect".
Tl;dr, I wish the book were a bit longer, and that it spent time clarifying the ambiguities of the different sphere levels.