Really, really, unexceptional (2-2)

I believe the answer is:

so-so

'unexceptional' is the definition.

'really really' is the wordplay.
'really' becomes 'so' (both can mean 'extremely').
'really' becomes 'so' (both can mean 'extremely').
'so'+'so'='SO-SO'

(Other definitions for so-so that I've seen before include "Of middling quality" , "just about adequate" , "Barely passable" , "Rather middling" , "Tolerable, indifferent" .)

I've seen this clue in The Guardian.

Want a hint initially instead of a full solution? Install my app