Although the program is free, don't think that it's a poor program. The GIMP has become very famous and that's not a fact of luck. The GIMP is very useful, powerful and fast. It can be used as a simple 'paint' or as a full and professional photo editor.
We have to highlight its flexibility, because you can adapt it to your style of work. It is said to be the free Adobe Photoshop.
The GIMP includes lots of features that until today were included only in very expensive programs, so, now that they are free, it's time to use them.
The GIMP is becoming more and more famous because of its powerful functions, and of course, because it is totally free.