The tricky point of torsion level, or any interconnected suspension is this: get the car to translate vertically when hitting a bump rather than rotate about its center of gravity.

With interconnection the car is effectively suspended at its CG --Schwerpunkt. Thus an individual bump encountered by either the front or rear wheel will cause the car to rise vertically rather rotate about its CG first to the rear then to the front as the front then rear wheel rides over it. The moment of intertia of the car in vertical translation is much greater than its moment of inertia in rotation so the effect of the bump is much less.

You can see that in the picture Craig just posted. The TL car actually rotates about its CG (usually known as "pitch") much less than the older car. There is actually a really good explanation of all this in the Packard Film "The Safe Road Ahead".