Gosh, what a success! (3)
I believe the answer is:
wow
This clue is a double definition.
'gosh' is the first definition.
'what a success' is the second definition.
(I have seen 'Huge success' mean 'wow' so perhaps 'success' could also mean 'wow')
(Other definitions for wow that I've seen before include "Impress hugely" , "Exclamation of surprise or praise - a palindrome" , "Amazing thing" , "Palindrome exclamation of astonishment or admiration" , "Expression of surprised admiration" .)