The pace of a story is key to creating an exciting ending.
What I mean by pace is not how fast the action takes to get going--even though that's important. I'm thinking about what it takes to let a story unfold. This would include what actions are important and when.
The significance of the actions will dictate the timing. Trite interactions will slow down the story even though they may enrich character development. It's a wonderful balance the author must orchestrate.
Then finally, there's trust. In the final chapters the pace has been established. The author allows the actions to unfold in the rhythm created, but something's different. The story changes from a tale to a revelation. The pace will now create the tension for the anticipated ending.