A few thoughts: Though not as weird as other things directed by Ken Russell, this is a pretty bizarre science ficton movie with awesome effects and an intriguing concept. Based on the book by Paddy Chayefsky who also wrote the screenplay (under a pseudonym), it's no surprise that this is a very clever story with strong characterization. William Hurt gives what I would consider to be among his best performances ever (rivaling Kiss Of The Spider Woman and A History Of Violence) in a role where he's required to go to more insane and committed lengths than a majority of his other performances. The visual effects are totally awesome, blending body horror into the affair in subtle ways, and the result feels like a blend of Kubrick and '80s Cronenberg. It's never boring, moves along at a decent pace, and keeps things interesting at all times -- both visually and storywise. I particularly enjoyed the blend of scientific and natural elements, which keep the story grounded while still fantastical. It's not the most groundbreaking film, but it was interesting to watch and very well constructed.
Who would I recommend it to? Fans of cerebral sci-fi, body horror, and movies with unique visuals. And since it's written by Chayefsky, it's pretty intelligent.