From publisher blurb:
Volume IV introduces FEATS to your OSR game with a unique means of how they are limited yet potent to those players that wish to invest in them for their characters. In addition, two classes are presented, the barbarian and the shaman. And finally, rules for player characters to produce some of their more stockier magic items, potions, scrolls, wands, and staves.
86 feats are presented within these pages, ranging from Agile Dueler to Weapon Mastery. While a few refer to previous options provided in earlier BX Game Option Volumes, they can easily be ignored and still have a plethora of feats available for the players to choose from. And the option makes them completely optional, characters do not automatically gain a feat at specific levels, but must invest in them as desired.
While the Barbarian does generally exist as a playable class in most OSR systems, this version is just a bit different any may be a worthwhile alternative. The Shaman is a spellcaster similar in vein to Druids as far as worshipping Nature and the spirits within, but several new spells are also given to help flesh out the Shaman's more spiritcentric nature as well as the ability to craft totems and fetishes.
And who doesn't want to play a magic-user that creates his own potions, scrolls, wands, and staves during his down time? If the character has the time and funds, it is possible to try and produce such needed items, though success is not guaranteed.