I actually ended up watching this the same night as The Book of Eli. Though you'd think two films set in post apocalyptic futures featuring raving bands of thieves and cannibals would be similar, the two are drastically different in tone. This is mostly because, while The Book of Eli had a significant amount of dark moments, The Road is completely morally nihilistic and uncompromising in its grimness.
Just to be clear, the trailer above is much more action packed and conventional than the actual film. While other films portend to be about the end of the Word, The Road is about the complete and utter decimation of civilization. When the plot is centered around the conceit that somewhere, anywhere there must be something resembling goodness in the world, you know you are in for a rough couple of hours.
The Road is very much worth seeing, you just might not want to watch it in a double feature with Grave of the Fireflies.