What are different interpretations of the roads ending? Please see below.
I've always seen the ending as hopefull; The boy finds a new familly who demonstrate to us that the story of the man and the boy carrying the fire is not an isolated one. Furthermore the boy's prospects seem improved, he gains a motherly figure in his life, company of those his own age ( which he expressed a wish for with the missing boy) and a generally better equiped lifestyle in a world where possessions correlate strongly with survival.
How can the books ending be interpreted differently, ie as a despairing one?
There can be many different interpretations of the novel, The Road. The very fact that the books leaves you without a solid conclusion makes the mind of the reader explore different avenues. You took te book in a very hopeful way. The boy's loss in a sense is also matched by gain, namely, others who will carry on the flame. However, not all people will be hopeful as you for several reasons.
First, the world is a desolate place and who knows if life is even possible in the long run.
Second, if you think about it, the boy and those with him are the exception of humanity and not the norm. Most people are without morals and only for themselves. They have been reduced to animals. In light of this, what makes a reader think that there is hope?
In light of all these points, I can see how people are decidedly pessimistic.