I'm writing this assuming that everyone knows that an episode review thread is full of spoilers...
I've had others quote the book where it definately doesn't come across as all out rape as it depicts in the show; Cersei wanted it but not next to the body, but Jamie "insisted" and she finally relented, telling him basically "yes, yes, hurry" and reached down to guide "little jamie" inside her.
The intention of the show's producers was to show you "You're not supposed to really like these people", and showed a bunch of these characters being assholes... like fat knight/fool betraying Sansa's trust and was only in it for the money, little finger then killing him etc, and they changed the twins' scene to rape as just another bad act on Jamie's part and a bit of punishment for Cersei.
They didn't anticipate the twitter and tumblr activists going absolutely nuts because the show is full of child killing, murder, burning people alive at the stake, child sacrifice, off-screen rape.
I personally don't care about the change, Cersei and Jamie are both incesty inbreeding evil cunts. I know they're complex and have circumstances, but they're more evil than sympathetic now and nothing absolves them of the results of their actions.
He tried to kill a kid, murdered his own adoring cousin to escape just a day before being released, and has done other awful things through is his life... She took pleasure in tormenting an innocent naive girl, desires to kill her own family, killed people herself, took joy in suffering peasants and like the others, would kill anyone standing in the way of power.
She deserved it and they both deserve whatever horrible fate they get just like their evil inbred offspring Joffery... no one was trying to make excuses for a teen who enjoyed killing things and ordered the death of kids (He was the victim of a mental illness brought on by incest after all), but he deserved his dreadful poison death or even worse.