This seems to have been the consensus reached by many of Joad's contemporaries. Indeed, in his obituary in the Times of London (April 10, 1953), we are told that Joad 'had no interesting contribution to make as a philosopher.' He is then characterized as an 'author, university teacher, controversialist, and entertainer'.
His lack of originality is borne out by the two main on-line encyclopedias of philosophy (the SEP and the IEP), in which the only discussion of Joad's views appears in Paisley Livingston's entry on the 'History of the Ontology of Art'. (Joad's works are cited, though, in a number of entries.)
Joad does seem to have excelled as a philosophical journalist. His expository gifts were noted by reviewers as diverse as Michael Oakeshott, Cyril Connolly, W. R. Inge, A. C. Ewing, Evelyn Underhill, H. L. Mencken, and even Bertrand Russell (who otherwise had only contempt for Joad).
One of Joad's virtues was his interest in non-western philosophy, especially Indian philosophy, about which he wrote a popular book. According to one bio,
Joad looked to eastern philosophy as an antidote to western modernity. He attended a number of Sarvepalli Radhakrishnan’s lectures and wrote on his philosophy (Counter Attack from the East, 1933). He also wrote a book on Indian civilization (1936) assisted by Girija Mookerjee.So, as a philosophical journalist Joad covered more than just his own home turf. He opened Britons' eyes to another philosophical tradition. And, at a time when Churchill was expressing his wretched views about Mahatma Gandhi, Joad published 'The Authority of Detachment and Moral Force: Mohandas Gandhi'. This paper was included in a volume that Radharkrishnan edited in 1939, Mahatma Gandhi: Essays and Reflections on His Life and Work.
Joad's coverage of philosophy was certainly biased -- he was a Platonist about pretty much everything -- but it helped some very bright individuals to find their way into philosophy. In his autobiography, Antony Flew (e.g.) credits Joad's books as having spurred his philosophical development. Also, in his 'Intellectual Autobiography', P. F. Strawson says that he first experienced the 'intellectual pull' of philosophy partly by way of 'some popular books on philosophy (notably by the not contemptible C. E. M. Joad)' (Freedom and Resentment and Other Essays, p. xvii).