Deep Work is all about large blocks of time allocated to highly creative/in-depth work. GTD is more of a way of handling tasks that are obvious and known in a methodical way. Deep Work is probably more applicable to software developers or other creative fields than it is to say, someone like a secretary that has to manage a huge influx of tasks that fly in from all directions, most of which are trivial to handle, but can be "paralyzing" when not handled.