Well turned out? Weren't lacking interest! (4)
I believe the answer is:
dull
'lacking interest' is the definition.
(I've seen this before)
I can't explain the rest of the clue.
Can you help me to learn more?
(Other definitions for dull that I've seen before include "Not exciting" , "Overcast or uninteresting" , "Matt; overcast" , "Lacklustre" , "Gloomy" .)