Painter X is the program I use to paint digitally. When you want to simulate traditional materials, or do some really smooth blending for art that needs not to be scaled, go to Painter. It takes .psds. I use it for my soft shading because it does the painting effects I want in far less time than photoshop.
At times, it is harder to figure out because it has slightly different shortcuts. The eyedropper tool is D, but I changed it to I like in photoshop. It has so many built in brushes to get the proper effects you want. SO many brushes. Its overwhelming at times. But you just have to explore them. I have barely touched oil brushes because right now it's not right for my arts.
Sometimes it crashes. Kinda annoying. It crashed a few months ago. But then again, photoshop, firefox, ALL adobe products, and internet explorer all crash. So that's not new. It has autosave.
The main point of this post is to say that layers are dealt with differently in Painter X. You 'collapse' layers instead of 'dropping' or 'merging' layers like in other image programs. To drop a layer means to merge the layer with the background layer. Be careful in that regard!
To collapse a layer in Painter: Press Ctrl + Shift + X, and the program will merge the current layer with the layer just below it.