Well GIMP is just fine for what it is a free photo editing program. It in no way compares to PS/CS. Aside from the obvious fact it's free, the user face takes a little getting used to, but some of the general advantages I would say are 1) it's updated more often than PS. 2) Being open source, it's very customizable, and there are always new user-developed plugins & tweaks & twerks being released.
Gimp is not easy to use but once you learn is a good tool. I am using the XP-Pen Artist 12 Pro ( xp-pen.com/product/479.html ) display drawing pad for Photoshop . It’s the best thing I ever did for photo editing. It’s seriously amazing.