Anticlimactic (adjective)
Lacking climax, disappointing or ironically insignificant following of impressive foreshadowing.
“After all the build up, the ending of the story was an anticlimactic letdown.”
Anticlimatic (adjective)
misspelling of anticlimactic
Wiktionary
Anticlimactic (adjective)
causing disappointment at the end of an exciting or impressive series of events
“it was an anticlimactic finish to the match”
Oxford Dictionary