I had the oppertunity to handle one of the new Gen 4 Glock 22's this week. Here is my opnion.
The most noticible difference I saw on the new Glock is the grip. The texture on the Gen 4 is similar to the RTF, although not as agressive. The dots are larger but fewer in number than the RTF, a pleasant change for those with soft hands. The biggest difference was the addition of changeable backstraps. Small is standard with a medium and large size able to snap over the frame. The mag release button is more than double in size compared to the older models, extending towards the rear of the grip to assist those of us with smaller hands; and it's able to go to the other side.
The slide serrations on the RTF did not make it onto the Gen 4's as they retained the standard vertical ones. There is a small "gen4" engraved on the side of the slide behind the model number as well. I did not notice if the slide lock was ambi or not (I am right handed).
There is a rumor that the sights will be upgraded to steel instead of plastic however the model I saw had the standard plastic ones.
Nothing else was new from Glock other than that, would like to see a Model 34 RTF or a reintruduction of the G25 and G28?