Is krita any good?

Yes, although its focus is more on the painting side than photo-manipulation.

For me, it does everything I would normally do in PS (and some things it does better), and there is no question that it blows the other free alternatives available out of the water by a huge margin (e.g. GIMP) with features like animation, CMYK (and other colorspaces), HDR/high-bit-depth, OpenColorIO integration, a nice brush-engine, etc

Massive potential, and immensely better than GIMP.