Often times people reach too far or change too much about a series. It's not that 3rd parts are automatically despised; it's that writers/producers/whoever decide that the original concept isn't good enough. They feel a compulsive need to make it 'better' and they often fall flat on their faces while doing so.
There's plenty of trilogies that do a great job of maintaining and improving on their core product. Indiana Jones and the Last Crusade was the best of the trilogy(Yes fuck you, I disown the 4th.) The Return of the King was a fine end to the films and the books. So was the Bourne Ultimatum, Back to the Future 3, Grand Theft Auto 3, even Revenge of the Sith was the best of it's set of 3.
People just really dislike it when an otherwise good series gets fucked up by the ending. They add in Ewoks in some retarded nonsensical Cameronian appeal to bows are somehow better than laser rifles. They make Spiderman act like an idiot, turn emo and start dancing down the street while singing. They add a villain with a ridiculous voice that's difficult to take seriously; scenes where armed terrorists with assault rifles get charged by cops with shotguns and hand guns and everyone starts punching like they forgot how guns work; and an ending that doesn't work because Bruce Wayne is hugely rich/famous and would have been recognized very quickly. Mass Effect 3 randomly jumps you with a weird ending that breaks good writing conventions by introducing new characters and random new ideas that where thematically contradictory to the entire direction of the series. Fallout 3 contradicted the tone, lore and ignored the writing style of the previous games. Assassins Creed 3 moved away from the parkour free running and added the series most boring protagonist who whines about how killing is wrong while being an ASSASSIN.
There's plenty of trilogies that do a great job of maintaining and improving on their core product. Indiana Jones and the Last Crusade was the best of the trilogy(Yes fuck you, I disown the 4th.) The Return of the King was a fine end to the films and the books. So was the Bourne Ultimatum, Back to the Future 3, Grand Theft Auto 3, even Revenge of the Sith was the best of it's set of 3.
People just really dislike it when an otherwise good series gets fucked up by the ending. They add in Ewoks in some retarded nonsensical Cameronian appeal to bows are somehow better than laser rifles. They make Spiderman act like an idiot, turn emo and start dancing down the street while singing. They add a villain with a ridiculous voice that's difficult to take seriously; scenes where armed terrorists with assault rifles get charged by cops with shotguns and hand guns and everyone starts punching like they forgot how guns work; and an ending that doesn't work because Bruce Wayne is hugely rich/famous and would have been recognized very quickly. Mass Effect 3 randomly jumps you with a weird ending that breaks good writing conventions by introducing new characters and random new ideas that where thematically contradictory to the entire direction of the series. Fallout 3 contradicted the tone, lore and ignored the writing style of the previous games. Assassins Creed 3 moved away from the parkour free running and added the series most boring protagonist who whines about how killing is wrong while being an ASSASSIN.
