Concluding event strong, considering everything is a little lacking (5)
I believe the answer is:
final
'concluding' is the definition.
(synonyms)
'everything is a little lacking' is the wordplay.
'everything' becomes 'fin' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'little' indicates taking the first letters.
The initial letter of 'lacking' is 'l'.
'fin'+'a'+'l'='FINAL'
'event strong considering' is the link.
I am not very happy about this link. Some or all of it may belong to another bit of the clue.
Can you help me to learn more?
(Other definitions for final that I've seen before include "Last in a series of games or contests" , "Coming at the end" , "The last exam or leg of competition" , "Conclusive" , "Last, ultimate" .)