Here we have multiple stories from various comic strains boiled down to the version of Eddie Brock infected by the Symbiote virus. In the very first introduction of Venom, the virus infects Spiderman and adopts some of his skill and later spins off to become the arch rival of Spiderman. He is dangerous to Spiderman, since he can't pick him up on his Spidey sense. The movie is based on the later version of Venom, where Eddie Brock is infected with the Venum virus. Here the movie changes it up to be an alien virus discovered by Life Organization in order to further the human species. Unfortunately, the virus has a similar plan to overtake the planet after getting back to the home planet.
As we all know a lot of the film is CGI with only the villains being shown in action against a CGI Venom likley done with stunt men off green screen. So the main character really only plays the parts where he is partially or wholly human. They have the slow build of Venom slowly taking over his body, but Eddie is in control to later when Eddie has very little control of the parasite as he calls it. I think the journalist story plays out well and we see why the character is drawn into the justice of Venom's ruthlessness.
Who is the villain in the film?
Do you think this movie could have been made without CGI?