Pretentiously impressive (9)
I believe the answer is:
grandiose
'pretentiously impressive' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for grandiose that I've seen before include "affected" , "Ridiculously impressive or imposing" , "Impressive in style" , "I grade son as affectedly splendid" , "Impressive, magnificent" .)