Well the opening sequence kind of frames things in terms of adventure serials, so when it returns to it in the latter half of the film its not out of place. And then it still pauses for a breather with that TERRIFIC scene of Indy and Marion on the ocean liner. You know, just some character bits for ten or 15 minutes. And even then it never really gets back to the "serial" formula, I mean Indy threatening to blow up the ark is just his character, and theres no serial precident for what happens at the end, it just Spielberg comic-book craziness.