"Good going!" (4)
'good going' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for nice that I've seen before include "Pleasant - French resort" , "Amiably pleasant" , "Fine as in distinction, or pleasant" , "Riviera resort locals call 'La Cote d'Azur'" , "Pleasant Riviera town?" .)
(Other definitions for nice one that I've seen before include "very good" , "like it!" , "Congratulatory phrase" .)