You also might want to add an extra joint at the ankle. You will need to bend the model there, and a joint, like the other bend points, would make that more robotic.

Another thing that can help some with robots ...

Mess about with just putting a skin modifier on the toros and head sections. Then, attach the arm and leg pieces as seperate objects with no skin modifier, to the respective bones. On stock models, where they wanted rigid bits of armour they do this. The game makes no effort to stretch or deform the mesh when the bones move.

It's a different effect to play with!

Otherwise, make sure you have plenty of polygons around the joints where things are going to flex.

Finally...hip joints. The stock anims treat them as ball joints rather than a simple hinge. Be careful with the detail design there so it moves in a natural way.