Over here in the UK at least, "Camelot" is hardly known. In truth the only reason I know it is because Julie Andrews is in the original broadway cast. "My Fair Lady" is loved everywhere and frequently revived, and indeed Julie Andrews features more prominent in the original cast recording for that show - if she be its popularity magnet that is.
I have never seen the musical, but for what I've read it seems the libretto is rather challengingly protracted. The music though is a jewel. It really sparkles with the shine of Camelot: of mythical, royal England. As such I can see why "Camelot" might not have been as popular as "My Fair Lady". Originating in the States, only a popular piece of entertainment would become endearing in the long run; the vigour of Bernard Shaw's "Pygmalion" - to which it adheres to more than "Camelot" to T.H. White's "The Once and Future King" - induces "My Fair Lady" with rather more uplifting music. If you like grace with a touch of regal air, though, the music of "Camelot" is no less good. Julie Andrews is the only once-in-a-lifetime instrument here, but her befittingly complemented presence makes for an unforgettable experience.