Complex opens with a traumatic 'Much Ado About Nothing' (1,5,2,1,6)
I believe the answer is:
a storm in a teacup
'much ado about nothing' is the definition.
(I've seen this before)
'complex opens with a traumatic' is the wordplay.
'complex' indicates anagramming the letters.
'with' says to put letters next to each other.
'opens'+'a'+'traumatic'='opensatraumatic'
'opensatraumatic' anagrammed gives 'A STORM IN A TEACUP'.
(Other definitions for a storm in a teacup that I've seen before include "Much Ado about Nothing" , "too much for a trifle" .)