What it really comes down to is character. Mystery Inc. is one of the first times in the 43-year history of the franchise that anyone’s been allowed to develop the gang as characters, and it’s something that changes the entire tone of the show.
Before Mystery Inc., they were really just archetypes with few additional twists added for the sake of gags, like brainy Velma who always lost her glasses. But with Mystery Inc., the characters are rebuilt from the ground up, with individual motivations, new relationships and interaction with each other that go beyond one person telling another how the mysterious fog was really created by dry ice. They even get actual families that exist for a reason beyond providing a rich uncle with a haunted ski resort. They’re fully realized for the first time.
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