In a word: brilliant.
This is without doubt or hyperbole the very best fantasy RPG campaign setting that I have ever read (and I've read many!).
Wolfgang Bauer and his team have delivered a dark reflection of old world myth and legend and given them a richly-detailed home in Midgard. The usage of real-world elements is just familiar enough to give the place a strong sense of the believable--there are gnomes and Baba Yaga, for instance--but they've been re-imagined in ways that seem fresh and new. The elves are nearly extinct. Familiar gods wear masks to conceal their machinations. The gnomes have sold their souls to the infernal in hopes of escaping Baba Yaga's vengeance. And the cannibal hag herself isn't what you expect! The result is that Midgard feels like it could be a genuine place for your heroes (and villains) to call home.
This gorgeously-illustrated volume contains rules for both Pathfinder and the AGE systems, but isn't dependent on them: the designers have wisely kept the rules information to the minimum required to guide the GM and players. It could be adapted with ease to any system. I can't wait to use this setting as the foundation for a new campaign!
[5 of 5 Stars!]