It must be both a blessing and a curse to be Brandon Cronenberg. On the one hand, your father is the top name in psychologically-intriguing body horror movies. On the other hand, that's a huge shadow to step out from. After making a decent impression with his debut feature, Antiviral (a film many people enjoyed more than I did), Cronenberg looks like he may be about to solidify his reputation among horror fans with Possessor, a dark and bloody movie that is arguably much more horror of the mind than anything to do with the body.
Andrea Riseborough is Vos, an assassin who takes over the bodies of other people, via an implant, in order to get to her victims. When the job is done, Vos gets the unwitting "host" to commit suicide, thus allowing her psyche to return to her body, which is housed in the machinery allowing her connection to the implant. Vos seems to be struggling with her own identity, understandably so, and also has certain attachments to items/people that may be an issue to someone in her line of work. This all comes to a head in her next job, when she's placed inside Colin Tate (Christopher Abbott). Tate isn't as easily controlled as others, but maybe that is partly to do with Vos not necessarily wanting to immediately return to her own body.
The start of Possessor is certainly a sequence that immediately draws in viewers, showing the assassination M.O. of Vos and then adding enough little details for things to be pieced together. And the end of Possessor is quite jaw-dropping. This is a film book-ended by moments that you won't forget, with Cronenberg showing an ability to deliver real shocks that aren't just delivered in a vacuum. The middle section is where things are a bit problematic, with a number of scenes that are surreal and dark, but not as interesting as the more energised moments around them.
Cronenberg has a bit more room to play here, or so it seems, compared to his debut, and he doesn't squander the opportunity. There's a cast that also includes Sean Bean, Tuppence Middleton, and Jennifer Jason Leigh in small roles, and there's a feeling of a more completely-realised movie world here than there was in Antiviral. Dialogue may not always seem to make sense, but a lot of it is loaded with more meaning that becomes obvious on a rewatch.
Riseborough is very good in her role (although I remain convinced that she isn't now able to take on a role without knowing that it satisfies a certain misery quotient). Even while not seen onscreen, her quiet and cold performance, and how the script conveys this, means that you always feel her presence. Abbott is equally good, and in mostly the same way. He may be onscreen a lot more than Riseborough, but he's portraying someone not always in control of his own actions or thoughts. Everyone else already mentioned does good work, but it's Riseborough and Abbot who own the movie.
I rate this very highly, despite my problems with the middle act. That's how effective the rest of the film is, and how unique it feels. I've not seen anything that caused me to react so strongly in a long time, and a film that can manage that deserves a fair amount of credit.