However, Children of Men is admittedly not as bleak as The Road, so not a fair comparison. If you really want a film that produces bottomless despair in the viewer, I recommend Threads (1984) instead. It was produced by the BBC on a shoestring budget, and yet it's still a better film. I can't say I recommend it, but if you do watch it, the ending is on par with Requiem for a Dream for being memorable and filled with doom and horror.
The Road just wasn't very good IMO. No Country for Old Men, on the other hand? Same writer, different genre, but excellent.
Mind you, I didn't think it was samey or cliched, I don't remember thinking "there are too many of these already". What I thought was that it was poorly written and uninteresting, and that it seemed like bleakness for its own sake.