It doesn't get near as much attention as the 9 vs 40 vs 45 debate, 1911 vs Glock, or the "Is the P320 a weapon of ass destruction or the best thing since Saint Browning bestowed his blessing upon us" debates...
there is contention and debate among fanboys - Beretta dust covers. Old school 92's, 92FS's, and the M9 have straight dust covers. To my eye, they even angle downward slightly. I personally find them fugly. That one area ruins the lines and sleekness of the overall design.
They changed the frame in the 90's because .40's were cracking Beretta frames like they did Glock locking blocks - Glock went to their three-pin design. Beretta beefed up the frame around the locking block. Since they use the same frame between 9's and 40's - that change carried over to the civilian 92FS and variants. The M9 remains with the straight dust cover, because government regulation is so damn retarded that it'd damn near take an act of congress to allow the upgraded pistol to be phased in, even if everything else remained the same, despite the fact that these guns are functionally identical.
If you note on the image above at the back of the grip - the backstrap on the old frame is also not radiused / blended into the grip - whereas the mid 90's-onward guns, the backstrap is melted into the grip for a more comfortable feel.