Gen 2 vs. Gen 4

So,
Picked up a Gen2 G19 and G23 a few months back....sent into Glock, had them refinish the slides, add new night sights and refresh the internals. Aside from the finger slots on the grips, is there a major difference between a Gen 2 and 4? I guess what I'm getting at is the question whether there is anything in the Gen 4 that makes it more accurate, durable or functionally better than a refreshed Gen2?

Many thanks for your help.