The G is quite a bit larger.
The iris diaphragm on the G has smoother edges.
The camera used for the comparison photos was a Nikon D80.
I used aperture priority single area autofocus for all shots, aiming the focus point at the same spot for all comparisons- I felt that was the best way to ensure uniformity. Sometimes the G made a slight difference in shutter speed exposing 1/3 stop longer.For all comparison photos, as above, the G is on the left and the D is on the right.
Closing the aperture a bit, the D seems better saturated, and you can see the advantage of the G's iris diaphragm in the out-of-focus highlights.
Pretty much even at f/8.
It's gone by f/2.8 on the D but the G is picking up some red fringing.
More severe red fringing on the G at f/4, not on the D.
More chromatic aberration at f/1.4 on both lenses but different colors. 100% crop.
Gone by f/4 on the D, not so on the G. 100% crop.
Gone on both lenses by f/8. 100% crop.