In terms of extras, there is a commentary track from Stephen Farber (film critic), a booklet, a CD with four songs (just to whet your appetite), trailers, and a few featurettes. The first of these pieces combines real archeologists digging for the ruins of Camelot alongside making-of footage of the film. The second is a half-hour long TV presentation of the opening of the film in New York City. Not truly interesting for what it says about the movie itself, it is terribly interesting to watch the premiere unfold (including what seem to be the original commercials). There is also an excellent making-of piece which not only talks about the film and it's production, but larger questions of what was happening with Warner Bros. at the time and the state of the film industry as a whole. It is an excellent history lesson and well worth one's time.
Camelot is worth watching for the soundtrack alone. One may be amazed at the sets and costumes, but the story of Arthur has been told better elsewhere and on more than one occasion. No, the reason to watch isn't the story, it is simply to hear Harris and Redgrave sing, and no one would fault you if you simply skipped from song to song to do just that.