The Matrix
A series of movies that was absolutely the most awesome thing on earth...until the last two minutes of the third movie when the whole thing got shot to hell, along with all of my admiration for the Wachowskis.  Actually, NOTHING got shot to hell.  That was the problem.  A freakin' TRUCE?! Come on!
At least Neo died.  "I know kung fu."  Give me a break.