Singer's album downloads exceed low expectations at launch (5)
I believe the answer is:
adele
'singer's' is the definition.
(Adele is a singer)
'album downloads exceed low expectations at launch' is the wordplay.
'at launch' suggests taking the first letters (first letters begin or 'launch' words).
The initial letters of 'album downloads exceed low expectations' is 'ADELE'.
(Other definitions for adele that I've seen before include "Woman" , "Female singer from London" , "Singer with albums titled 19, 21 and 25" , "Performer" , "Popular female singer" .)