There are a number of parameters you will want to adjust for maximum effect. One is the shape of the texture ramp for both the shell and the shell edges. A linear ramp produces a somewhat abrupt cutoff; tapering the beginning and end of the ramp will produce a smoother transition. The texture ramps can also be adjusted by changing the texgen eye plane. Changing the plane values can move the distance and the range of the cutaway transition zone.
Since both the shell and the interior of the object will be lit, there is some question as to what the back surface of the shell revealed by the cutaway should look like. As before, aesthetics and the surrounding scene will determine what's best. Some choices would be showing the back of the shell in a darker version of the shell's color, unlit. Another possibility is to use back face lighting on the shell's interior.