Krita, while originally focused on painting, is also worth a try for image editing. It has effect layers missing in Gimp, and an easy to grasp GUI.

In terms of UI or actually under the hood?

I've found PhotoGIMP makes GIMP UI more like Photoshop, which helps me a lot: https://github.com/Diolinux/PhotoGIMP/releases

On a Mac I switched from Photoshop to Pixelmator no problem. Hoping PhotoGimp can help me do the same.

Photoshop CC runs in wine as of the last time I checked, although I think some tweaking was needed?