Well for one thing it is WAAAY more efficient that GDI/GDI+ in almost every area since it works through the Direct3D interface...So if you are doing a lot of intensive vector drawing you would get much better performance with it.
I note that there are some very interesting and unique functions available that are not (easily) implemented using GDI+ only, such as the various gradient brushes, and "Geometries."
In addition to basic drawing primitives such as points, rectangles, and ellipses, Direct2D provides the ID2D1Geometry interface for describing simple and complex shapes. Interfaces that inherit from ID2D1Geometry define different types of shapes, such as ID2D1RectangleGeometry for representing rectangles, ID2D1RoundedRectangleGeometry for representing rounded rectangles, and ID2D1EllipseGeometry for representing ellipses.
More complex shapes can be created by using the ID2D1GeometrySink interface to specify a series of figures composed of lines, curves, and arcs. The ID2D1GeometrySink is passed to the Open method of an ID2D1PathGeometry to generate a complex geometry. ID2D1SimplifiedGeometrySink can also be used with the DirectWrite API to extract path outlines of formatted text for artistic rendering.