I greatly prefer the Gen4 over the Gen3's and I have numerous Gen3's. I have medium sized hands and I could not reach the mag release on the Gen3's without breaking my grip. Not an issue on the Gen4's as I can reach the release but I do prefer an extended release. I also prefer the texture of the Gen4 over the Gen3. Hated the RTF versions. I also like the dual recoil and prefer the impulse. Many do not notice a difference, but I can easily distinguish the difference. I really like it in the Gen4 G21. I had one of the earliest or first 1000 run of the Gen4 G17 and it did develop a brass to face issue. I ran over 25K rounds through the weapon before I changed out the RSA and ejector and that made a big difference. Had video on it, but it is no longer.
I like to swap sights, go with a minus or 3.5, standard spring and a polish job. Yes the trigger will smooth out with time, but not as effectively as a polish job IMO. I can definitely live with a standard 5.5 out of the box but I can do all the way up to changing trigger geometry and getting down to about a pound and a half if I chose, but that is not my preference. 3lbs minimum is about where I like to be. Ironically several years ago during one of my Glock armorer recert courses, Dennis Tueller who was the instructor actually taught me the technique to accomplish the really light trigger. I ran my Glocks for many years with non modified frames and did very very well with them. Now I personally like to do a full custom hand fit where I remove finger grooves, slightly reduce the backstrap, undercut the trigger guard, radius the trigger guard, flare the magwell and texture the grip. The beauty of the Glock is similar to the AR where you can easily and effectively (if you know what your doing) alter the weapon for a true hand fitted pistol. Cost, easily customized to fit to the shooter, accuracy and reliability and it is hard to beat a Glock pistol.