It wasn't so much the regular scifi thriller stuff that got to me? It was definitely the body horror aspects of what happens to people infected by the protomolecule. But I found that the way they filmed it was generally, agreed, much less horrifying than the descriptions in the book. Also, I think the way it's presented feels more like the rock-in-the-pond that causes the ripples that spur the plot, rather than overpowering everything else like it does to me in the books? But it's definitely a YMMV thing.