First advice, keep it short, try to say what you want to say in a few lines. Unless the artwork is brilliant people won't read that much.
Lore is important for character design, understanding of the story will help you create something interesting that fits.
I never played the Fallout games so I can't judge the character, but it seems like a standard mutant. I am sure you can come up with something else. Try making allot of sketches and pick the things you like from those to make your final illustration.