The most disappointing movie I've ever seen? "Avatar" is the answer to that question.
Yes, it may sound like I'm hating the movie just because everyone else seems to love to hate it, but I just couldn't get over how shallow and manipulative the story was, I mean, the performances were good, but the characters and plot were so boring and predictable.
That and the aliens were way too perfect to be an alien race, I mean, the design is just so lazy just to pull every trick in the book to make them more sympathetic to the audience. I just thought it was lazy design to be honest, along with everything else on Pandora. Yes, the effects were spectacular, but the design of everything was a bit too 'magically' for a world based in reality such as the weird floating rocks and the light up forest.
I also just couldn't get over the forced theme and moral of the movie. Yeah, District 9 had an obvious theme and moral of racism, but it wasn't like it was shoving it down your throat the entire movie.
Along with that, it didn't have any real gray area to speak of. All we had was the stereotypically evil military general and the asshole corporate CEO to portray the humans as an evil and destructive race of planet killers. While we had the Na'vi portraying a perfect race in complete harmony with nature.
Then it just got kind of stupid near the end like the large mech having a comically large knife, yeesh.
Again, this movie just disappointed me with how shallow and manipulative it was. It was by no means a horribly movie, but I just didn't like it at all and came out of the theater disappointed.
The most deceptive movie I've seen was "Inglorious Basterds." Now, I loved this movie, but most of the commercials and advertising portrayed it as a movie about a bunch of guys killing Nazis. I was expected a bit more action, but still enjoyed the dialogue none the less.
It was good, but I'm still slightly sore that it tricked me.