I don't actually understand how a phone screen over 4" is beneficial in any way. In my experience with larger phones and tablets, it just blows up apps and buttons to be overly large and spacious. The size doesn't add any increased usability aside from maybe allowing for more text to be viewed on the screen at one time.
Personally, my large hands have absolutely no trouble tapping the necessary buttons on my 4" iPhone (aside from the notification center x's). I don't mind scrolling on my phone to see content, either. The tradeoff of having a phone so large that it becomes awkward to use and hold is not worth it.
Maybe I am being naïve, but there is absolutely no benefit to a larger screen aside from seeing more text and unnecessarily larger elements. I'm convinced that this demand for a larger screen is simply because people are starting to believe that it is a must. Somewhere in the recent years, the idea has been created that if the screen is small, it's inferior, which makes no sense.
I give the screen trend 3 or 4 years until people begin realizing that monstrous sized phones are unnecessary and inconvenient.
Apple played it right. 4" is just fine. As for the quality, I have absolutely no complaints. I have yet to see a better display (although I haven't really been looking at competitor displays in person)