Asa work in progress it is looking better and better. Unfortunately I have no idea at how how much GIMP can do, as I use Photoshop.

Some suggestions any way, would be to add some texture to the blood lake and the land outcroppings.

In Photoshop you can use the Patternstamp tool to lay down the patterns. Another cool way is to use Bevel and Emboss and use the Texture setting, then draw in your pattern with the Patterstamp tool and it can give you 3D texture and feel. No idea if or how to do the same in GIMP.