I just really vehemently disliked the decision to kill off Robb and Catelyn. After reading like two and a half books, the driving impetus behind the whole thing felt to me for the remaining Stark clan to finally reunite and to give the Lannisters some comeuppance (perhaps with the help of Danaerys). Gets you all invested in the characters and then kills them off for little return other than the "shock factor", and a big part of the reason to actually keep reading the series is gone.