You know your Dad, so you are the best one to suggest or not suggest a sequel. But you might try showing him Legion.
But first explain the trepidations you’ve expressed in your post here.
Then – because Legion is directed so differently from Friedkin’s film – you might “soften the blow” by explaining that there is a certain amount of visionary/symbolic/surreal stuff in Legion that was not in the Friedkin film. You might explain the early scene of Miller’s narration as the camera moves down the Georgetown street toward the MacNeil house at the end of the street – and a man in a priest’s cassock runs twice across the street. He’s hard to see because of the credits, but we are obviously meant to think that this is Karras – or Karras’s reconstruction – of himself on the night of the fatal exorcism.
You might also prepare your Dad for Scott’s grouchy and gruff Kinderman, as compared to Cobb’s more kindly version. Certainly a word should be said about the expanded relationship between Kinderman and Karras in which Karras is now Kinderman’s “best friend”, an intimacy that did not exist in the original film. Also you might emphasize that Flanders, not Fr O’Malley, is now playing Fr Dyer.
That said, you might ask your Dad to just be patient and wait for the best stuff which is yet to come, namely, Kinderman’s confrontation with the Gemini – the scariest part, and the core, of the film.
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