I will keep my summation brief as you will have either seen it already or read the synopsis.
What lies beneath this entire film, is the question of memory. How accurate is it? How reliable is any single person's account, of anything! What is truth? It's reflected in the philosophical teachings and comes into play within the context of a mystery thriller. In addition, what is guilt really? If a large number of people say something is so, does that make it real? Does having a personal philosophy have to match up with one's own actions?
The film raises these and other fascinating questions. I would hope that one would walk away wanting to explore philosophy in more depth. However, for the average popcorn going movie goer wanting their 'thriller' spoon fed to them, they will of course be disappointed.
Those seeking a little more substance will find this satisfying, playing out, exactly as it should.