I can't think of a word that would summarize this phrase into one coherent adjective. It's for a thesis I'm writing about a musical composer.
Well, there's perspicuous:
Clearly expressed or presented; easy to understand
You'd definitely get points for using a difficult word to mean easily understood! I'd recommend:
Of which I personally prefer
accessible - easily understood or appreciated.
There is a term, used especially in connection with complex or technical material that may suit: user-friendly
easy to use or understand
What's wrong with 'easily understood'? 'Lucid' could be a possibility in the right context. As far as 'relating to the common man', you could say that something was 'an everyday expression' or something that would be understood by 'the person in the street'. If you used 'perspicuous' in an undergraduate essay the tutor marking would probably not know what it meant and would have to stretch for a dictionary. It is a fine line between using expressive language and using over-flamboyant or slightly archaic language. 'Perspicuous' clearly falls in the latter category, in my view.