Horror/science fiction films have rarely been singled out for the quality of the acting in them. Over the decades, a couple of "monsters" have been tapped for praise: Fredric March won an Oscar for his turn at Jekyll and Hyde, & Jeff Goldblum was rightly seen as an example of "inspired casting" in David Cronenberg's remake of _The Fly_.
But I think Richard Wordsworth has them both beat.
I enjoy _The Creeping Unknown_ overall, but it is Wordsworth's performance as Victor Caroon that lifts it into the stratosphere for me. I mean, sheesh, _look_ at him! This is an incredibly painful and, yes, passionate portrait of a man whose _body_ is being taken over and is changing into something else, even as he fights to retain possession of it. What might such a battle _feel_ like? Wordsworth lets you know, and in doing so anchors an almost cliché science-fiction "what if ...?" in raw human nerve endings. Watch him battle the frightening desires that overcome him; watch him try to stay ... human. He's first class, and why his career never really took off ...
I am probably all alone on a windswept plain in this, but I think Wordsworth's acting here is as frenzied and solid as that of Klaus Kinski in any of the great movies he did with Werner Herzog. So shoot me! :)