Total Recall (1990 film) = Finished

You'd think narrative ambiguity would make things easier for you, right?
You just don't say how a story ends. 

That isn't true, of course, as I've learned through much pain. If anything it makes your job harder. You have to justify alternate timelines and evolving viewpoints. You have to have certain conclusions resolved in your head, before you can lead or mislead your audience. It's all the difficulty of creating a traditional story, drawing a (hopefully interesting) line from point A to point B, combined with the arrangement and rearrangement of chaff so the person experiencing your work is confused for the right reasons.

Considering this narrative doubt is Total Recall's entire point, its approach to the process is intriguing.

In Total Recall, there are a few major moments where Quaid's reality could be interpreted as a dream, or a lie, or some manner of manipulation. These moments are reinforced from varying perspectives, make narrative sense, and are treated with gravity when they come up. However, like the rest of Quaid's obstacles, they are eventually overcome. The movie has chosen its course. Total Recall's hero wins, and these moments of doubt are left to lie where they died.
They're left to fester.

By alternately raising and then disregarding points to be made against its own narrative, Total Recall encourages the viewer to struggle against alternate interpretations of its events several times over. Whatever you want to believe about what really happened in the movie, the destroyed cases against its story leave rubble in your mind. The story is told--definitively so--but the doubt initially seeded remains. So, the more obsessive the viewer in question is, the more this doubt rankles and sticks. It's a brilliant implementation, honestly.

The more you want the truth, the less likely you are to find it.

You ultimately doubt yourself.