The first city supplement for the Scarred Lands, this book was a shot off the bow of most d20 fantasy games, which had cleaved extremely closely to standard D&D in hopes of capturing a larger portion of the market. Instead, Hollowfaust makes a bold statement about necromatic magic, which the players must navigate not necessarily to survive (it's a city - city environments, by their definition, are hospitable to many different kinds of people), but to thrive in the way that D&D pushes its characters to thrive. You won't just feel like you're in Fantasy Canada (the Forgotten Realms - a setting I love) when you come to Hollowfaust. You will feel the pressure of magic and possiblity on the world in unusual and eye-opening ways. GMs will find that Hollowfaust lets them talk about how ancestors and memory both empower and are exploited by the present.
If I had to name something to improve about Hollowfaust, it is that the city is a fantasy city first and a D&D city second, perhaps the only area where it doesn't excel. There are many areas of pressure to explore which D&D heroes will have no means of fully interacting with. In a way, it's more of a fantastic experience than D&D, with its romantic and escapist nature, can ever embrace.
It's perhaps the best fantasy citybook of the d20 era, and well worth your time.