Well, the power of the novel is to create a sort of metaphor of the world that Mc Carthy has created in all his books and that this metaphor is never more than the awareness of what is in front of us.
In that sense, "The Road" and "Blindness" (the novel of Nobel prize "Saramago") are two mirrors of the same image but with a different landscape. Saramago shows that landscape is secondary (the movie of Meireilles is also good at showing this), while Mc Carthy insists on a landscape but this is also secondary and a simple metaphor.
Unfortunately, John Hillcoat has decided to focus strongly on the digital transfer of Mc Carthy nightmare, with the result of a succession of nightmarish landscapes (but finally boring, because they are visualized and not imagined!). In its search for the fidelity to the text he has lost his own personal contribution to the movie (see the great difference with the other Mc Carthy recent adaptation: "No country for old men", showing both Mc Carthy and the personal vision of the Coen's).
Finally, what the book is excellent to do...leaving us in the incertitude to understand if this is a real landscape, a remote part of our mind that cannot be even imagined, in a sense a metaphor of what Mc Carthy has described in his other books, then the movie is totally incapable to represent.