I own several Gen4 Glocks in various calibers, and have fired several more, but unfortunately, I have not yet had a chance to shoot a Gen4 Glock 17. The new Gen4 Glocks in 9mm seem to have slightly heavier springs than the older Gen3s, so in some cases, owners must use full-powered ammo for best functioning results. All the Gen4 Glocks I own and have fired have been flawless with ALL ammo types, but a few folks have experienced problems with the cheapest ammo types and the some Gen4 9mms.
I usually tell folks that unless they have a specific need for one or more of the Gen4 features (lefty mag release, smaller grip), they might be better off sticking to the Gen3 Glocks for a 9mm with a proven track record.
"Placement is power" -- seen in an article by Stephen A. Camp
(RIP, Mr. Camp; you will be remembered, and missed)