Optically the Nikon AF-S Nikkor 80-400 f4.5-5.6G ED VR is completely different from the previous model, 20 elements including 5 of ED (Extra-Low Dispersion) or Super ED Glass arranged in 12 groups (formerly the lens had 17 elements in 11 groups, with 3 of ED glass). The DxO Mark score of 22 makes this the best super-zoom yet tested: 4 points above its predecessor. The individual parts of the score are good for the new lens too: sharpness at 14P-MPix is just one point behind the Sigma 120-400 f4.5-5.6 DG APO OS HSM Nikon but the Nikkor scores better overall and much better for chromatic aberration.
There are other areas where the new Nikkor is better than the old, it utilises Nikon’s Nano-Coat Technology for reducing flare and even more crucially the AF on the new lens is driven by a SWM drive which is pretty quick, on the old lens AF was driven from the body, meaning that AF was not possible using some cheaper Nikon cameras. On the down side it is heavier and bigger, but it is a 400mm lens and the extra weight seems to be justified by the extra quality.