The final part is over. Great! (5)
I believe the answer is:
omega
'the final' is the definition.
(I've seen this before)
'over great' is the wordplay.
'over' becomes 'o' (cricket abbreviation).
'great' becomes 'mega' (I've seen this in other clues).
'o'+'mega'='OMEGA'
'part is' acts as a link.
I am not very happy about this link. Some or all of it may be part of another bit of the clue.
Can you help me to learn more?
(Other definitions for omega that I've seen before include "Athenian character" , "character in Greek literature?" , "Last (Gk. letter)" , "character from Athens" , "Greek long 'o'" .)