It is free and available to everyone. It offers basic tools that can be sufficient for basic image editing. The interface is quite simple.

Free, powerful, customizable image editing.

I like first and foremost the simplicity in using GIMP, the completeness of the tools, and the organization of the tools on the workspace. I appreciate the fact that, despite being software that doesn't have much to envy from the more renowned ones, it is still open source. Even for a self-taught beginner like me, it is possible to produce a sufficiently presentable work. Moreover, the initial setup of GIMP was very simple.