Operetta delights one, or otherwise (3,10)
I believe the answer is:
the gondoliers
'operetta' is the definition.
(Gilbert and Sullivan operetta)
'delights one or otherwise' is the wordplay.
'otherwise' is an anagram indicator.
'delights'+'one'+'or'='delightsoneor'
'delightsoneor' is an anagram of 'THE GONDOLIERS'.
(Other definitions for the gondoliers that I've seen before include "G&S operetta" , "opera" , "Gilbert and Sullivan operetta" .)