Love very good Greek character (5)
I believe the answer is:
omega
'greek character' is the definition.
(letter from the Greek alphabet)
'love very good' is the wordplay.
'love' becomes 'o' (In tennis, 'love' means 'zero').
'very good' becomes 'mega' (informal term for excellent).
'o'+'mega'='OMEGA'
(Other definitions for omega that I've seen before include "Foreign character" , "24th Greek letter" , "long letter" , "character in Greek literature?" , "Last thing" .)