Start, Middle, Ending? Wheres the ending?

Rating: 7/10 (15 October 2014)

So last night I went and saw the highly rated film "Gone Girl", I had REALLY high expectations of the film as it was hyped by many critics as being one of the films of the year, also the talk of it possibly being nominated for an Oscar.
I had NOT read the book before going into this film and watching it.
The acting was perfect, Ben Affleck was actually superb amongst a cast who aren't really known for making Oscar worthy films (Tyler Perry, I'm talking about you). The film started off great however after about 30 minutes I found things started to get strange (plot wise). The characters weren't natural and it seemed like an "out of whack" "exaggerated world".
After the plot twist is revealed mid film, the movie started to go down hill and down hill fast. If you're waiting for an amazing twist at the end, where your jaw drops and you go "Oh ma gawddd", hold off any hope, there is nothing coming (You get your twist mid film and its not that great).
I was majorly disappointed with the ending and I don't want to give much away, however lets just say I rushed home and searched up forums in hope to see if I had missed something important.
For those who HAVE seen the film, half way through the movie I developed this theory and was hoping that there was going to be a twist at the end where we find out the whole movie is a horribly written crime/mystery novel by Amy who has a failed career as a writer. It would have summed up all the cheesy, exaggerated and unnatural scenes that we see through out the film.. Like the woman who wants to take a selfie with Nick and the fact Nick has sex with a 20 year old so publicly in his sisters living room at night.. Did that not just seem comical to anyone? It would have also been perfect because in the film Amy was a Harvard University graduate, so to see her in reality as a failed novelist would have contrasted perfectly, of her living in this non-existent world, with a made up husband that she could get revenge on (Nick being symbolic for how unfair the world is).
I rate the movie 7/10 purely because the start and middle of the film carry the ending on its shoulders, keeping you entertained and guessing, even if there is no classic, twist plot ending, you still have hope.