As a photography enthusiast that works with raw camera images I have not found a better free alternative in Linux than Cinepaint. The fact that it can use Adobe's color profiles is good, but even better is its support for 16 bits per channel. That gives one a lot of leeway when editing pictures. Here is one example.
This is what came out of my camera:

This is how it looked after adjusting it with Cinepaint:

I love being able to process the image all the way through in 16 bit mode, including the sharpening step. I only go down to 8 bits for exporting as JPEG.
The problems with it are the clunkiness in the interface. For example, why can't it remember the place where an image was opened from? Instead, it make one have to path all the way back every time one wants to open another image and even to save the one already open (from RAW). That is my biggest gripe I guess. The other little things I could live with. So, that is my take on it.