I wasn't sure what to expect from this product in terms of quality. IMO, there are too many publishers out there in the table top market who seem to think short, generic resources are worth as much as some of the meatier products. I'm pleased to say that this is a well rounded product that offers something for everyone interested in adding aquatic elements to a campaign. I recommend it along with Alurria's Cerulean Seas (which has underwater combat rules).

What I liked:

1. A wide variety of resources that will work in many different types of campaigns; you can get a lot of mileage out of this product.
2. Being a fan of Oathbound, my Ceptu now have competition from several underwater non-humanoid races. This a good thing.
3. Hazards and spot checks by depth zones. The Underdeep had officially kicked off some really nasty campaign ideas.

The only criticism I can find with the book is that the city section could have been a lot longer with more history and flavor, but it's pretty difficult to include that kind of information in a book that's going to focus on a lot of different areas.

If you like Planescape, you owe it to yourself to check this out. This is a great setting for multi-dimensional goodness and fun with almost ludicrous attention to detail. The art is great, the layout is professional, and it's just plain fun to read.