They had a recoil spring "upgrade" (recall) early on, and made a change to the ejector... there were assorted comments about other MIM parts having issues, but to a much lesser degree. Those are the only frequently commented upon issues I'm aware of.
Funny thing about Glocks... they are so many out there and so typically reliable that when something does go wrong, there is, what I feel, a disproportionate number of negative comments on the internet. Those comments are usually followed by 25 "my gun works fine" comments... but no one remembers those.
On a personal note... I'm not a Glock fan by any stretch of the imagination, and since they started putting finger grooves on them in the Gen3 series, I stopped even trying to like them because they simply do not feel good in my hands.... but, disregarding my personal views and looking at the big picture, I could do a hell of a lot worse than having a Gen4 Glock 17 in my hand when the SHTF... and in the 9mm Luger caliber, not much better.
Shoulder Drive Nicholson Club