In the past seven years, each new advancement in iPhone camera technology has made dramatic improvements to image quality. The iPhone 6 is no different. Besides being faster to shoot and easier to focus, the images taken with the iPhone 6 camera show greater detail and are significantly better in low-light.
Interesting comparison. The iPhone 6 camera is vastly superior in several areas and is particularly amazing in low light. However, it also surprised me that in other examples, like daylight photography and portraits, the results between 4S, 5, 5S and 6 are almost indistinguishable from each other.