The Economist has a very good article on some of his work; you should read it if you haven't done so already. I quote:
Dr Ritchie likes to emphasise that he was just one member of a group. With characteristic modesty, he suggests that many of the improvements he introduced when developing C simply “looked like a good thing to do”. Anyone else in the same place at the same time, he implies, would have done the same thing.
In other words, he Did the Right Thing; he found the answer that is, in retrospect, obvious. That is the mark of a genius.
His ideas stood the test of time. He has reached a local maximum: Java or C++ or C# are object-oriented languages; C is the procedural language. Sure, there may be something better than C, in some sense of the word. It's like Newton's laws being surpassed by Einstein's relativity – C will still be there. Still valid, still useful, still used.
We have lost a humble genius, a mathematician, an architect of the abstract. It's sad that most poeple will never be able to appreciate the beauty of things he has done. Perhaps that, too, is the mark of a genius.