Simple, but effective.
You can add realism by adding a bit of a swinging action to the robot’s upper body (shift the hips left and right) and you can make the robot body bob up and down with the low point of the up/down movement when the robot leg is outstretched and the high point when it is mid-stride. If you make it so that the body weight is always more over the leg that is in contact with the ground then it will give an impression of mass to the robot. Since it’s a robot, you could break down the animation into abrupt sections. ie. Shift weight to left leg, move right leg forward, shift weight to right, move left leg forward, etc.
A slight bending at the elbows due to momentum of the the lower arm adds realism to an organic character’s walk, but you might not want this for a robot. Maybe your robot could be programmed to simulate this in an exaggerated way?
As people walk, they bob their heads from side to side and up/down slightly and this adds realism to an organic walk cycle. Again, maybe your robot would not need to do this, but could simulate it by the head bobbing up/down like on a spring or shock absorber.
There are loads of ways to add realism to a walk cycle suck as twisting of the hips, twisting of the body, bending of the spine, twisting of the neck, a little bounce in the body due to the shock of the foot hitting the ground, the arms swinging outwards a little due to the body twist rather than just forwards and backwards, rolling of the shoulders, etc. etc. The best thing to do is walk about and see how you move. Watch other people walking (but don’t stare ;)). There are good walk cycle tutorials out there to use as a starting point, but they are no substitute for observation and practice.