Can you describe a book so brutally, gut-wrenchingly bleak as 'great'? I guess there is hope in the love between father and child protagonists (though even this is as agonised and desperate a portrayal of that inter-dependency as you will ever read) and there is just the possibility of light at the end of this terrible journey, but it's fair to say that more optimistic takes on the human condition are widely available.
A book to make you think, and shiver, and draw your children closer. Masterful. A film of this will be out soon. Read the book first.