Org is great because it's plain text, but at the same time offers outlining, timestamps, tables, links and lots of other features. Following Emacs tradition, it doesn't impose any workflow on you. It just gives you some primitives to build the system you want.
A great feature of Org are programmatic views of your data, possibly from many files at the same time. Some are already implemented, but still customizable, like Org Agenda. I use Org Agenda to have a Kanban-like view of my projects. I can simply see all WIP tasks, approaching deadlines and events in a little plain text window.
That's, I think, the minimum viable productivity system. You have a list of projects with tasks, some deadlines, some events and some inbox. You select a few tasks to do every day, like Ivy Lee suggested, and you do them. You want to see these plus deadlines and scheduled events which can be easily achieved with Org Agenda.
A GTD-like system would tag tasks with contexts, and offer some context-specific views, but I find that's too much work. Another pitfall of GTD, in my opinion, is that it doesn't encourage WIP limits which eventually makes it overwhelming.
I credit GTD with popularizing the need for an inbox, the task-centric view to time management, and the distinction between tasks, tasks with deadlines and events. But I think GTD leads to too much planning waste, projects broken into tasks that get constantly outdated.