I have a 2017 GTI sport with 6 speed manual transmission. It's generally been good, but I had to replace the clutch at 17K miles. (Sorry, not operator error -- first time I've had to replace a clutch since I began driving manual transmission cars in 1985.) The dealer repaired the car under warranty (invoice says "release bearing is sporadically applying pressure to the pressure plate and causing the clutch disk to slip"). I have heard stories of others having clutch slip issues inside the warranty period, but not getting repairs since it's considered a wear item.
I've also noticed a few odd sporadic things, like the ventilation not working correctly once, or the entertainment system jamming a few times -- both fixed by "rebooting" the car, i.e. turning everything off and restarting. (Ventilation apparently not mechanically controlled, even though it's manual). Nothing too serious.
Generally it's a quality car that seems extremely well built (I disagree with the earlier comment about Mexican build quality -- there may be differences between cars built in Europe vs. Mexico due to different suppliers, but I don't think you can say the European ones are better.) But it also seems complex, so not sure how well it will hold up over the years.
The Golf R is more complicated than the GTI Sport, with more systems that can go wrong. My guess is that it's a great car for 5 years, and who knows what happens after that.