Above all it's a good round quantity (9)
I believe the answer is:
paramount
'above all it's a good' is the definition.
I can't tell whether this defines the answer.
'round quantity' is the wordplay.
'round' becomes 'par' (I can't justify this - if you can you should give a lot more credence to this answer).
'quantity' becomes 'amount' (amount is a kind of quantity).
'par'+'amount'='PARAMOUNT'
Can you help me to learn more?
(Other definitions for paramount that I've seen before include "More important than anything else" , "Pre-eminent - movie maker" , "Highest" , "Chief in importance, supreme" , "Of the greatest importance" .)