I was very pleased with the content of Path of Shadows , and I would buy it again after having read through the material.
One of the things about many 3rd party material that makes me cringe is that it is often seemingly too powerful to integrate with base PF stuff. There are a lot of great ideas, but independent developers just go over the top with their implementation.
Well, that is not true at all in this case. The Nightblade class, shadow themed archetypes, feats, spells, & weapons all are nicely developed and would seemingly easily integrated into a standard pathfinder adventure with core/base classes. I wouldn't hesitate to allow this material in games that I ran.
The spells alone are extremely well developed and should be part of any shadow mage's arsenal, and the Nightblade class looks very fun to play.