I drive using the rover's built-in cameras almost exclusively for the sake of realism/immersion --only switching to the orbit camera when I get really disoriented. But when driving like this, it is very difficult to determine the grade of the terrain. As a result, I often end up on the side of a hill without even realizing it until I begin to slide down it.
I would like to see the vehicle's pitch and roll displayed on the HUD. This can either be in the form of an artificial horizon (like in an aircraft) or simply as text values listed in degrees (from -90° to 90°).