"Ripley" was not made in haste: the photography, the locations, the design, all look great. The basic plot skeleton was written well enough almost 70 years ago, and no screenwriter could really destroy it.
Instead of reveling in all that is melodramatic, sexy and intense about this story, he chooses to treat it with matter-of-fact dryness. It is possible that it is precisely this loyalty that exhausts "Riply"; But of course it may be the choice to ask the cast to deliver their lines in a tired and unenergetic tone.