From the publisher's website:
Everyone loves rolling a high initiative when a combat starts. Going first is its own reward, allowing a player to get the jump on foes, grab points of tactical advantage, and set the tone for the combat to come, but it’s also just fun. Finding yourself at the bottom of the initiative order is significantly less exciting. For low rollers, the combat round can seem to lag on, having little to do but watch while other players accumulate memorable moments. Sometimes a player going last doesn’t even pay attention to the action until it gets close to his time to take a turn, assuming he can “catch-up” once his character gets to go. This often leads to delays as players must have recent combat events explained, need time to look up rules for whatever action they decide to take based on that update, and get feedback from other players who now aren’t paying attention until it’s close to their turn. The longer it is between player turns the more likely players are to tune out, which only adds to the length of time between turns.
The whole game goes much smoother and is more enjoyable for everyone when all the players stay involved mentally, actively absorbing the current action while waiting for their own moments of glory. That is much more likely to occur when there is some kind of combat action that the character can perform at any time—a way to occasionally jump the queue and join the battle right now. (Just think about how much more attention a player pays if his character has delayed his action.) Even if such options have consequences, the possibility itself encourages the players to stay focused on what’s happening at all times so that they’re able to react quickly when they can make a difference. To that end, we need a way for characters to perform actions out of the normal initiative order, to link its use to specific combat situations so players want to pay attention, and to make sure the cost of doing so is high enough that it’s not happening every round, but low enough players feel taking such an action is worthwhile.
A look at Chapter 8 of the Pathfinder RPG Core Rulebook reveals an interesting combat option—between “swift actions” and “miscellaneous actions” is the very promising sounding “immediate action.” The immediate action fills all the gaps we’ve identified; it just needs of broader set of options. To answer that need, we present a new set of immediate action feats—feats that give characters new actions they may perform in specific situations if they are willing to spend an immediate action.
The Genius Guide to Feats of Immediate Action gives characters more potential ways to act when it is not their turn, encourages new tactical opportunities to spice up game play, creates a more flexible and reactive battle field, and gives players a strong incentive to pay attention throughout the combat round.
Nobody likes waiting for their turn and with immediate action feats you will never have to wait for your turn again.