It told you everything you just saw didn't happen due to the literary use of unreliable witness. It also put the Kevin Spacey character in a completely different light, from the poor victim you've been watching for over an hour to criminal mastermind. It was brilliant.
So 90 minutes of nonsense is OK because you’re told at the end it didn’t happen? There was nothing terribly interesting about Spacey’s character to begin with to make him any more interesting after finding out who he was. In Fight Club the twist at the end truly turns it into a different film with different themes. Here there’s no reason to ever watch it again. The use of the unreliable narrator is a lot more complex than what they did.