Most important features of a man a gal hoped to change (5,3,5)
I believe the answer is:
alpha and omega
'most important features of' is the definition.
The definition suggests a singular noun which matches the answer.
'a man a gal hoped to change' is the wordplay.
'to change' indicates anagramming the letters.
'man'+'a'+'gal'+'hoped'='managalhoped'
'managalhoped' is an anagram of 'lphaandomega'.
'a'+'lphaandomega'='ALPHA AND OMEGA'
Can you help me to learn more?
(Other definitions for alpha and omega that I've seen before include "Two extremists literally" , "identifying with God?" , "Extremist characters in Athens" , "The beginning and end (of the matter)" , "used to describe the deity" .)