Try not to intentionally stare at it, but if I do and it becomes hostile, I would have bow & arrows ready.
It seems like they would spawn only at night or in caves (at least where there's enough room for them) judging from the screenshots. And hopefully they would burn in sunlight like skeletons and zombies.
I am going to isolate an enderman in a glass box so I can observe him. Then I will test his properties, see what he does, check out his reaction to other mobs (ex. can he harm other mobs? If so, what will they do about it?), then put him in a room with charged creepers and a skeleton, and stand on the top edge of the box. That will be funny.