Full Disclosure: I recieved a complimentary copy of this product for review purposes.
While this product was released long before Eldritch Witchery, this product feels like a B/X version of the material presented in the previously mentioned supplement. That doesn't make it a bad supplement, though, by any stretch of the imagination. Having already read EW, I can see that Brannan's previous work also had similar sensibilities.
This is more than just a class book, it's really a campaign supplement that presents a single new class with multipule options, allowing an enterprising referee to pick and choose what aspects of the material they want to apply to their campaign. The level of detail and sense of grounding in real-world history gives the material a gravity and believability not often found in role-playing game supplements - especially fantasy gaming supplements. The Witch is fantasy that never gets serious, but nor too does it get pretentious or self-important.
In addition to a detailed, multi-dimensional class, The Witch also provides an extensive collection of monsters and magical items. This not only gives the sourcebook more usable content, but having these extras helps give the Witch class a stronger presence into an existing campaign world. By having hints of the witch through these devices and devils, the introduction of the witch to an existing campaign never feels like its falling out of the sky or being introduced out of the blue.
The Witch is one of the most extensive, detailed, and well written OSR supplements I've seen in a long, long time and I'd highly recommend it to B/X or retro-clone game. Even if you never use the class, the extras on top of that make it more than worth the price of admission.
[5 of 5 Stars!]