I really have no complaints that I didn't have from the start, other than lint getting in the headphone jack and usb-c port and affecting operation to a surprising extent. Which is not, strictly speaking, the phone's fault. Everything else is just as pleasant to use as it was on day 1.
Interestingly, I just handed down my GS5 to my kids to replace their ancient and dying non-smartphone. I was really, really tired of it when I got the G6 this summer. Tired of looking at it, tired of the home button, tired of the charging port cover, tired of the laggy slowness and general frequent "not working right" behavior and not-great battery life. After cleaning it up for them (not even a factory reset) I actually find it not horrible again. And of course to them it is all new and fantastic (which I'm sure won't last long).