Apollo Justice is a good answer because it actually ruins the character established in the first three games.
The best example I can think of though is Lunar: DS. It actively ruins the main focus of the story in the first game. Before playing that game, I never thought it was possible to ruin my memory of other games in the series simply by existing, but the story in it sort of undid how I felt about the story in the first game.
Still love the first two Lunar games though.
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Moops?
"I thought you were making up diseases? That's spontaneous dental hydroplosion."