I'm not a 2D guy, but you can do 2D animation in blender, or so i heard. Other than that, there is Krita, Pencil2D and opentoonz(Has support for 2D skeletal animation) Probably a lot of more similar software, these just the ones i heard about. Krita being the most popular i believe.
Anyways, anything would be better that Gimp, that shit is a nightmare to work with.