Robot should walk reliably for an extended period of time, the plots should prove the robot is stable.
No "cheating" should be used, such as applying the forces directly, only the legs should be used as tools for force exertion.
To make sure it is presentable, multiple velocities and tuning parameters should be tried, and most importantly, disturbance rejection and robustness testing in the form of making the model information given to the controller inaccurate.
Turning in place and stepping sideways would also be preferable.
Running is a plus as well!