Ride a wave that is excellent, but superficial (7)
I believe the answer is:
surface
'superficial' is the definition.
(similar in meaning)
'ride a wave that is excellent' is the wordplay.
'ride a wave' becomes 'surf' (I've seen this before).
'that is excellent' becomes 'ace' (ace can informally mean very good).
'surf'+'ace'='SURFACE'
'but' acts as a link.
(Other definitions for surface that I've seen before include "Plane" , "Outer or upper layer" , "Top side" , "Top part; outward appearance" , "Outside layer" .)