Movie or TV series endings, which do you believe were a bust?

I know people who really followed the Sopranos but were let down by the seemingly weak and anti-climactic ending. I remember I watched a short-lived series Kyle XY (or something like that) which I guess was not being picked up in the third season so the powers that be, tried to rush out an ending but it was messy and made no sense as to what was going on in the series up until then. Have you seen a movie or series that after investing so much time, the ending was as flat as warm root beer, or as muddled as a knotted ball of yarn?