For me, the tackle by Pepe is a red card since his foot is coming down on to Alves and if Alves doesn't move is leg away he could have been hurt badly or even had his leg broken. It's the cleats up or foot coming down type of tackle that has no place in the game.
Sure, Pepe might have not meant any harm, but it's just too dangerous to have your foot coming down on to another player like that. Did Alves exaggerate the play to draw the red? Yes, he did. But, it was Pepe who made the reckless challenge in the first place.
For me, Barcelona was trying to play throughout the match and Real Madrid was looking to foul. In many ways Barcelona must frustrate opposing teams as they keep the ball and make the other team chase. I think Real Madrid were getting tired of chasing.