Maybe Beowulf's a delight, upon reflection? (4)
I believe the answer is:
saga
'maybe beowulf's' is the definition.
I can't tell whether this defines the answer.
'a delight upon reflection?' is the wordplay.
'delight' becomes 'gas' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'upon reflection?' is a reversal indicator (I've seen 'upon reflection' mean this).
'a'+'gas'='agas'
'agas' back-to-front is 'SAGA'.
Can you help me to learn more?
(Other definitions for saga that I've seen before include "Soap opera" , "Long heroic tale" , "Long detailed story" , "Flag associated with a" , "Old story" .)