I'm always extra impressed with people doing digital stuff; I can't get my head around it! I need a pencil (or brush) in my hand or nothing comes out, lol!
Actually with a wacom tablet or I guess any other table, its pretty much like a pen and paper deal. I cannot draw with a mouse to save my life. Ive a friend who uses a mouse and paint, and is amazing! Once you get the art programs figured out ( I still have parts written down to help remember) then its pretty easy.
Wow, you are really good at drawing, Here is one of my drawings I did on the DrawSomething app. It's not really meant for realistic drawings, so this one is a bit different than yours.