re: Lots of relief, etc..,
I see what you mean, Raoul.
Even though the 'hole' is still dark as black, you can still make out the lower areas/layers of the rim and no, they are not reflections.
Nick's theory about the camera is a good one, but unless the crater is full of very reflective ice or (yikes) water, which is VERY UNLIKELY, it could, as he also said be a very deep void or be filled with some very black material.
Again, where's MOLA!