Nice trait, remarkably complex (9)
I believe the answer is:
intricate
'complex' is the definition.
(similar in meaning)
'nice trait remarkably' is the wordplay.
'remarkably' is an anagram indicator.
'nice'+'trait'='nicetrait'
'nicetrait' anagrammed gives 'INTRICATE'.
(Other definitions for intricate that I've seen before include "Convoluted" , "ornate" , "Entangled" , "Complex, labyrinthine" , "puzzlingly obscure" .)