Ben - nice pose and detail with a clean bg. I like that we can see the eyelashes and the whiskers around the chin. There's a yellow/green cast on my monitor.
Nice pose. Body side, head turned toward camera with slight tilt, bright eye on sun side. Soft late (or early sun), I like it a lot.
Surprised f5 was enough DOF to get sharp nose and ears. That prime 500 f4 a mighty nice lens. (And big!!!)
Not sure I see the color cast Rachel mentions.
Tom