Serious work of German, oddly receiving smuggled drug (5,5)
I believe the answer is:
grand opera
'serious work' is the definition.
'german oddly receiving smuggled drug' is the wordplay.
'oddly' indicates alternate letters.
'receiving' indicates putting letters inside.
'smuggled' becomes 'ran' (I've seen this in other clues).
'drug' becomes 'dope' (colloquial**).
The alternate letters of 'german' are 'gra'.
'ran'+'dope'='randope'
'gra' enclosing 'randope' is 'GRAND OPERA'.
'of' is the link.
(Other definitions for grand opera that I've seen before include "Piano concerti could be regarded as such" , "'Aida', for instance?" , "Musical entertainment" , "stage project" , "eg Aida, Faust" .)