Dreary, ugly? Oddly, on reflection, was attractive (5)
I believe the answer is:
lured
'was attractive' is the definition.
'dreary ugly? oddly on reflection' is the wordplay.
'oddly' indicates alternate letters.
'on reflection' says the letters should be written backwards.
'dreary'+'ugly'='drearyugly'
The alternate letters of 'drearyugly' are 'derul'.
'derul' backwards is 'LURED'.
(Other definitions for lured that I've seen before include "Seduced" , "Attracted" , "Tempted or enticed" , "was enticing" .)