Certain and uncertain endings

Alright. So early this week I watched Shutter Island starring a Mr. Leonardo DeCaprio.  Overall it was a very good film but that is not my concentration.  What I am concerned with is the ending.  I don't want to spoil the ending for anyone that has yet to see it, but I will say it is an ending that leaves the audience questioning what exactly happened.  It is one of those endings that you have to take an extra period of time and try to figure out what exactly just happened.

In this period of attempted epiphany, I instead came up with a general question.  Why do some directors or writers decide to end their films in a state of uncertainty.  At the same time, however, why do some choose to end in concrete or obvious endings.  Is it that one leaves a more powerful impact on the audience, or is it something more then that.  Could it be that they do not know a clear way to end it that will be memorable so they leave the ending up to interpretation.  Personally any ending that confuses me usually causes me to watch the movie for a second, third, or fourth time, or at least sit on the plot and try to figure it out.  However I do tip my cap to any movie that has a definite powerful ending.  When a movie has a straightforward, powerful ending (sorry I am drawing a blank on a specific piece) I tend to just sit there in a state of awe.  At the same time though, if the ending is awful or not what I was hoping for, I sometimes become enraged and don't want anything to do with the movie.  Very often people say things along the lines of "yea it was good, but the ending sucked".  And I feel this is a reaction many people leave with after movies.

 Sometimes many times an uncertain ending is the way to go, but I would say a powerful concrete ending is the way to go.  A good ending is what you leave the audience with and everything that happened for the last hour and a half or so goes out the window.  So what is the way to go.  Personally I feel like leaving the audience in a state of confusion is usually more powerful and leaves everyone wanting more, but if you are able to pull of the ending of the century that people don't hate, well then go all out for it.  Sometimes having some closure is the way to go.  I guess as the viewer, our opinion really doesn't matter and the ending is determined by the sinister writing and directing tactics by the people in charge of production.