Specific Feedback Requested
Any advice would be appreciated.
Technical Details
Nikon 200mm - 500mm @ 500mm
F/5.6 1/640s ISO 640
Hi Kristian, Great catch of the squirrel voicing his complaints. 
You nailed the focus on the face and eyes. I would have loved to see the comp include the tail, but you might not have had the time to do that. Also, nothing you can do about the busyness of the branches. You did nicely frame the face. I think your crop putting the face to the left of center and looking into the frame works well, giving the squirrel a bit of room to breathe.
Cheers,
David