I can accept some resistance to apocalypse now. It's a demanding watch and can test your patience but it's one of the greats so you might just have to eventually come to terms with your bad taste.
Also I wouldn't be so dismissive about the source material. Painting Coppola as the port-studio equivalent of a film maker is some pretty damning shit. My goodness. Patton was quite good and disqualifies at least that portion of your argument.
I haven't read shit from Grisham but I'll go out on a limb and say he ain't a high water mark for PROSE FICTION. What's usually regarded as low-brow reading is often turned into high-art films, not because the source was so good but the film turned it into something more. Like The Shining.
But I like Godfather III so maybe I'm not the best one to talk to about this.