Darktable's powerful parametric masks, combined with the ability to layer multiple instances of a module with a separate set of adjustments applied to each, makes it possible to quickly make high-impact edits. In the above example, using an additional exposure module to increase contrast around the picnic table draws your eye to this, the focal point of the image:

exposure

Next, a slight curve using tone equalizer gives more contrast to the surrounding grass between the areas in direct sunlight and those in the shade. Finally, using an instance of color balance rgb to add more blue to the shadows helps to provide more color contrast and another two instances to target just the saturation in the sky and leaves:

The improved contrast (both luminosity and color contrast) helps make this image much more dynamic. Moreover, using dodging and burning with the exposure module to direct the viewer's attention to the picnic table gives the photo a sense of structure and purpose.