I had a Gen4 G23, and I called Glock and got my replacement Recoil Spring Assembly shipped to my house for free. I still just didn't like the feel of it so I traded my Gen4 G23 for a Gen3 G23. I just seem to like the Gen3 better, but that's my personal preference. The Gen4 G23 did perform flawless with the 200+ rounds I put through prior to the trade.
My nephew had a Gen 3 Model 22 that fell in the dates of the rear frame rail issue, 2001 - 2002 I believe. It failed him on the firing line when qualifying for the Dept..
He purchased the Gen 4 to replace his Gen 3. I asked him what he thought, he said he didn't really notice much of a difference between the two and would still be carrying his Gen 3 if it not for the failure.