For me, GIMP is great for creating basic sketches and creating the foundation of your project. Unfortunately, because it IS a free software, there are some bugs and aspects of the software that hinder your work (ex: pressure sensitivity is no longer available in the new version, the software will randomly "experience problems" even though there seemed to be no problem when you were working, for some reason, the chances of the software crashing increases after 10 layers of so, etc.) but overall, I'd say that it's a good painting program for beginners to practice with before they move on to more complicated software such as SAI or Photoshop.