From one of my agile students, I got this about the differences between agile and more traditional methods. I thought it was well said, so I repeat it here.
It seems ... that the principle difference between "traditional" and "agile" project management is that the former relies on careful elaboration of the business requirements (project scope) and strict defense of that scope via change management
- this generally results in a long lead time between customer sign-off on requirements and delivery of the requested product - often met with customer comments "that's not exactly what I had in mind" or words to that effect.
[Agile] depends much less on a rigorous and well defended set of requirements (e.g. stories) and much more on delivery of product that can be reviewed by the customer much sooner and expectation of changes to those requirements based on customer feedback on the solutions as they are developed and delivered at end of sprint.