New diamonds, right? That's better! (5)
I believe the answer is:
nicer
'that's better' is the definition.
(I've seen this before)
'new diamonds right?' is the wordplay.
'new' becomes 'n' (common abbreviation eg NT for New Testament).
'diamonds' becomes 'ice' (slang term for diamonds).
'right?' becomes 'R' (common abbreviation).
'n'+'ice'+'r'='NICER'
(Other definitions for nicer that I've seen before include "more lovely" , "More pleasant or agreeable" , "relatively pleasant" , "Kinder; finer" , "comparatively agreeable" .)