You and I review party for returning neighbours - the difficulty is getting the numbers right (6)
I believe the answer is:
sudoku
'neighbours the difficulty is getting the numbers right' is the definition.
I can't tell whether this definition defines the answer.
'you and i review party for returning' is the wordplay.
'you and i' becomes 'us'.
'review' shows that the letters should be reversed in order.
'party' becomes 'do' (do is a kind of party).
'for' becomes 'uk' (I can't justify this - if you can you should believe this answer much more).
'returning' is a reversal indicator.
'us' reversed gives 'su'.
'uk' back-to-front is 'ku'.
'su'+'do'+'ku'='SUDOKU'
Can you help me to learn more?
(Other definitions for sudoku that I've seen before include "(Usually) nine-by-nine numbers puzzle" , "Number game" , "numbers in boxes" , "Boxing contest" , "Japanese number puzzle" .)