At its heart, Pathfinder (and many other fantasy roleplaying games) is about playing heroes who go on great quests to vanquish the forces of evil. Along the way, the heroes develop great powers and acquire awesomely powered magical items. Of course, there can be a lot more to it than just this: the heroes form relationships with other characters, both other heroes (the other player characters) and various other people (the non-player characters); the heroes can create items of their own; they can open businesses; they can fall in love. The breadth of possibilities is huge, but for the most part that heart of good heroes fighting evil remains.
Yet even that doesn't have to be immutable. Not every character a player creates in the game is necessarily good. There are nine alignments and only three of them are good, after all. Three fall in the neutral range, and many players will choose those alignments for their characters. They allow for characters who may not be bastions of goodness, but still rise up to fight against evil and save the day. But what if players don't want to save the day? What if they want to be the ones the heroes would normally fight against? What of the three evil alignments?
I'm not a big fan of evil campaigns myself, though I can see the draw. After all, the game is about pretending to be someone you aren't, and playing evil is perhaps the ultimate expression of that. And even if it's not the sort of thing you want to do all the time, playing an evil character just once to give it a try is a tempting lure (I have certainly done it). The difficulty with evil campaigns is that evil characters can have a hard time working together. It only takes one PC to turn on the others and suddenly the whole game falls apart—and possibly even the gaming group if some players aren't happy with what has occurred. But if you can get past the difficulties, then an evil campaign can have its own rewards.
Champions of Corruption is the third Pathfinder Player Companion book to take a close look at the alignments in Pathfinder and offer options for players playing those alignments. I was very impressed with the first two books, Champions of Purity and Champions of Balance, and so was greatly looking forward to this book. Even if evil campaigns are not my cup of tea, a discussion of evil in the game is an important thing, especially when there has already been a discussion of good and neutrality.