From the publisher's website:
The concept of a “critical hit” has been part of roleplaying games from the very start—an attack that is extraordinarily well placed or timed perfectly and, as a result, is exceptionally damaging. It started as a phrase used after the results of an attack were determined, but quickly made its way into variant systems and house rules until nearly every campaign had its own version. And in many of these systems, both what was necessary to inflict a “crit” and the results of that attack varied depending on the situation. And if you played under more than one GM, the chances were good that each one would have a different definition and set of achievable results for critical hits in his or he game.
With the arrival of the OGL and original d20 System games, critical hits became a codified part of the core rules. The details have changed slightly with rules updates, and again as with the development of the Pathfinder Roleplaying Game, but at this point there is an agreed upon definition of what constituted a critical hit. But, at the same time, a good deal of the mystique has been removed from the notion. Players now not only know exactly what is needed to achieve a crit, they also know just what the results will be—some extra damage. Certainly that has a tangible impact on the game, but it doesn’t fire the imagination or capture the visceral impact that many of the old house rules did.
The Genius Guide to Feats of Critical Combat works with the existing rules regarding critical hits, providing ways for players to put some of the “critical” back into their critical hits. Shatter shields, inflict disfiguring scars, achieve advantage over others on the field of battle—all these and more are possible effects for your character’s crits, depending on the feats you choose. Bring the shock and awe back to the battlefield, and remember the power of seeing a natural “20” on the die. Because while your characters can become masters of critical combat, so can their opponents!