More dice being cast? It's no great shakes! (8)
I believe the answer is:
mediocre
'no great shakes' is the definition.
(thesaurus)
'more dice being cast?' is the wordplay.
'being cast?' indicates an anagram (letters are dispersed or cast around).
'more'+'dice'='moredice'
'moredice' with letters rearranged gives 'MEDIOCRE'.
'it's' acts as a link.
(Other definitions for mediocre that I've seen before include "Ordinary" , "Come ride (anag.)" , "Not very good" , "Fairly bad" , "Of middling quality" .)