The example that really stings for me is Starcraft 2 (the overall games) , specifically Kerrigan and Raynor. Kerrigan was such a badass in Starcraft 1 and her turn to being a ruthless piece of shit when she evolves was one of the best parts of the series, her sudden change in Starcraft 2 gave me headaches , she turned into an irredeemable monster in Brood War that retconning that is one of the worst decisions Blizzard has made. In Raynor cases, I can't buy SC1 Raynor ever forgiving Kerrigan for killng Fenix (Dragoon), so SC2 ruins one of the most badass lines from SC1 (the one were Raynor says he will kill her).