This book has totally blown me away and is reminding about everything that is good about Robin Laws and Glorantha. It is well written (despite the customary Mongoose typos) and while richly satisfying it is also nicely constructed and a clear introduction to setting. I don't think Glorantha has ever been explained this well or in this detail.
It has me desperately wanting to crack out HeroQuest to give it a go. What about RuneQuest? Well until they actually have some rules for using Dragon Mystics in BRP there doesn't seem a lot of point yet.