1st generation guns had grips with a pebble like texture. no checkering of any kind
2nd generation guns got checkering on the front and backstrap
3rd generation guns kept the checkering on the backstrap, but added finger griives to the front strap, an acessory rail, and indents on either side of the grip for your thumb
there is also a 2.5 generation gun, that has finger grooves, and no rail
i personally prefer the feel of the 1st and 2nd generation guns, but the appearance of the 3rd generation guns