Here's a tip that will help you get rid of that soft washy, airbrushed feeling.

Make your painting larger in DPI and resolution.
For those that don't know, DPI means Dots per Square Inch in other words how many pixels are on the screen per inch. The more pixels, the smaller the squares and the smaller the brush can be which translates to detail.

To do this, go to the Rescale Painting setting under File and change your DPI to something more like 300 (Any higher and you might feel a lag in performance).

Alternately you could Resize the Canvas under File as well to something over 1800 and you will notice a marked improvement in detail that you can get.

Changing either of these settings really allows you to really get in there and paint with a small brush which will get rid of that soft airbrush feeling. Of course if you like that look then disregard this tip.

There are caveats in that now your brush will not be able to get as big as it was before but what I do is rough out a painting and then resize it to get more detail and then refine. I find it works well for me but maybe not for others.

Hopefully this helps!