Project Management is just as much about leadership as it is about management and in some cases it is more about leadership.
Regardless of whether you use an Agile or Waterfall based project structure, your management style doesn't change, simply the foundation of the project changes. How you lead the team through an Agile or Waterfall based project should stay consistent.
Having a leadership focus is fundamental in any successful project. Being able to create an environment focused on open communication, working together with an end goal in mind and having a clear understanding of what that end goal is.
What are we trying to accomplish? What is the primary objective? These are key quesitons to keep in front of the team.
Leadership is almost more important (at least to ETP) than whether you use waterfall or agile. Waterfall and agile, doesn't impact that leadership focus, regardless of methodology.
Leadership and Management
We tend to be so focused on the triple constraint of a project: scope, schedule, and budget that we turn ourselves off as project managers to leadership. This can be the biggest mistake in any project.
Project Leaders need to provide the inspiraiton and the passion to keep the project moving forward. To help your team overcome obstacles and remove road blocks. Road blocks are a key component for project leaders to address, regardless of waterfall or agile methods. You have to be someone that people can come to when they need something fixed or resolved, and if something is holding them up.
In some respects, the name should be project leader versus project manager as the success of any project truly comes down to leadership.