This is one of my fav textbooks about music theory and composition, and my favourite of the contemporary ones (I have several favourites that are no longer in print). What sets this one apart from other excellent similar books, is the fact that this has finally been written to be practiced at the piano. All the examples are for the piano except a few inevitable ones about counterpoint for more than 2 voices, which are written on multiple staves.
Best of all, most of the examples are at grade 1-3 ABRSM (just a guess, but I am pretty sure not unfounded). A couple of Schumann examples are at grade 5 or 6 at most. If you can learn grade 5 pieces easily and fluently, you'll find the examples in this book VERY easy, which actually makes learning music theory easier.
Moreover, most books of this type have workbooks that you have to purchase separately. I have nothing against that (all these books are very hefty, including the one reviewed here; these aren't superficial books like many of those new ones from Berklee Press). But this book comes with the workbook inside!
So especially if you are a pianist, or a piano student (same thing!) this is certainly the best contemporary book you can get about the subject. This book is for classically minded musicians who also want to get a bit of very detailed info about how the same techniques are used in popular music; not the other way around. This book is university level quality, this isn't some badly written book by hacks.
Of all the similar books I have seen or owned (these by Steven G Laitz, Stefan Kostka, etc, all excellent books), this is definitely the one I wish I had gotten the first time round. I always believed that you don't need to be shown a Chopin or Liszt example to understand how the chord of the augmented sixth sounds or what it does. No need to bother the greatest musicians ever to learn the alphabet of music. And while having a recorded real orchestra playing an example from a Mozart quartet on dvd is admirable, I prefer to read, hear, and feel at the piano. It's a bit like mindfulness and the (overrated) story of the raisin: you need to roll it over in your mouth, feel the texture, etc etc. I believe that with music theory is exactly the same.
For me, this book is a total winner, and worth every penny (or cent, etc). 10/10