This excellently researched adventure path takes the party through the nine worlds of Norse mythology culminating in the final battle of the Gods at Ragnarok.
This book it best used to run the campaign as intended. While you can certainly re-purpose the character options, magic items, and NPCs for other campaign settings, most of the location-based setting material is not as easily removed from the work as a whole.
What I like about the book:
1. I enjoy Norse mythology and this AP is true to the source material. If you love Norse mythology, you will enjoy reading, running, or playing in this AP.
2. Optional Magic Rules - I like how each of the 9 worlds affects magic differently according to the school of magic. For example, in Helheimr abjuration magic is decreased, but divination magic is increased. In each world, each school of magic is altered, augmented, decreased, or unaltered.
3. Variants of all player classes are provided as well as a new class: Rune Master. I've not yet run this campaign, but each class variant is flavorful and helps with immersion in the settings. Setting-specific backgrounds are also provided. Also, there are six clans that are detailed that provide additional background to root characters into the world. I would suggest that players be encouraged to select a setting-specific character and background options.
4. Other touches that help with immersion include an alternate alignment system where "good" and "evil" are replaced with "honorable" and "dishonorable" and a moral code composed of the nine noble virtues of the Poetic Edda, the following of which make a character "honorable." An additional skill is also included: Asatru (Wisdom), which measures a character's ability to "recognize and sometimes understand the energies, entities, and divine influences of the Nine Worlds."
5. The artwork is beautiful and evocative
What I think could be better
There are two areas where the book could have been improved. The first is that it could have been better edited. The book was first written in Italian and translated into English. For the most part, the English version is well written, but there are the occasional grammar errors that stand out. This is a minor issue that doesn't prevent understanding, but it does feel a bit sloppy in a book with otherwise impressive production values.
The larger issue, for me, is that it leaves much for the DM to fill in. That is fine for a setting book, but this is more an adventure path than setting book. Reading over the adventure, I can tell it will take more effort to prepare a session than a typical WotC adventure. Midgardr, which will be where the characters spend their time from 1st to 6th level, receives a good amount of detail, but the other worlds are only given summary treatment.
Even the section on Ragnarok is very short on detail. There are a number of encounters that can occur as the character attempt to complete tasks given to them by Odin as battles which the characters can have no influence on rage around them. These encounters have only a few lines of description and there are stat blocks for the foes, but battlemaps and tactics are up to the DM to come up with.
Even some of the mechanics require the DM to fill in the blanks. For example, the "altered" condition of in the optional magic rules states that "the effect of each magic is aesthetically altered depending on the World". That's it. There is no guidance or example. The WotC AP, Curse of Strah, did something similar with magic being aesthetically altered when cast in Barovia, but it gave a number of examples which is quite helpful to the DM.
In short, despite some minor shortcomings, if you enjoy Norse Mythology, you'll definitely want to obtain a copy.