overhead view
I took this image: MER-B_DIMES_1404m-B22R3,
enlarged it 3x, and cropped it.
As I see it, the best way in is to the lower left, at the notch. It appears that the rim is lower on the left side, the right rim is taller.
You are right Tom, note the discontinuous outcrops on the far side, and continous outcrop on the rim itself.
What interests me, are the twin bands (ridges) within the crater itself. Is this vertical bedrock uplifted and rotated by the impact that created the crater? (Google "Upheaval Dome") Is it down section? Or is it something else?
When Oppy get to the rim, we are going to get a great view and a better idea of what is in there...I can't wait!