Since the release of Matrix Reloaded, it has been quite rare for a sequel to be better than the original; but this film may be that rare exception.
The snake cinematography is excellent, giving the viewer a real sense of what it must feel like to be a giant snake hunting human beings. The use of color in this film is nothing short of brilliant. By changing the color of the lens (an effect that has rarely been used so well) the viewer is immediately aware of when he is seeing the action as a snake rather than as a third person viewer.
But there is also an interesting Roshomon effect going on as you switch between different anaconda perspectives, and realize that while some snakes might prefer one human for a meal, another might prefer someone a little different. This raises interesting questions about how we perceive race and gender.
But this movie isn't all action. In some sense, it is a cerebral meditation on the meaning of food and the way the desire to eat can drive us to commit great good, but also great evil.
There are frequent allusions to other great filmmakers such as Hitchcock, Kurasawa, Bergman, Tarkovsky, Eisenstein. There is one hillarious scene where one of the lead characters begins humming the theme from Jaws, and then a snake eats him. That is nothing short of brilliant!