I've not had a lot of experience in dealing with the HERO system, but have a member of my gaming group who swears by it. That alone was reason to do some digging to understand the system and whether this product added anything to the host of other fantasy books out there. At almost 500 pages, this does qualify as a Tome though, and shows what I come to expect as a comprehensive and fulsome treatment from the authors of HERO.
If you are only to purchase a single book about fantasy role-playing, this is a good contender. It is clear from the outset that the authors are not just casual consumers of the genre, and know fantasy intimately. There is an impressive annotated bibliography which put me to shame and has now formed a core reading list for the future. They effectively and concisely analyse the different elements of fantasy and investigate the key features of the fantasy sub-genres.
The rest of the book is dedicated to rules. Everything from character creation, archetypes, combat, magic, geographical effects and even morality is discussed in stunning detail. Given that a lot of HERO is based on designing specific instances from a generic idea, there is an underlying discussion of rationale which flows through most sections. I'm sure that any GM/DM who has previously run an FRPG will find some enlightenment from this book. Most of us never question why something is so in a game, so being forced to think about it is always a good exercise. The scope of the magic section alone should give even the most die-hard fantasy player pause for thought.
Overall, this is a very impressive piece of work. The authors clearly show a mastery of the genre, and write with an incisive style which is rarely seen in the hobby. The layout and artwork are both of a consistently high standard and should appeal to a range of tastes. The main warning is that this is a companion volume to the core rules for HERO system, you're not getting a complete game here. That said, I firmly believe that with a copy of this, the main rules and a homebrew setting (or even adapt one of the hundreds already on the market), you'd never need to purchase another book.