a new, distinct form factor, new materials, an even more robust design. the 5 was a stretched 4s, just like the x evolves the design from the 7. but it‘s the same basic design language, not like the changes between the 3gs and the 4 or between the 5s and 6. personally I prefer the period in the middle. Not as huge as nowadays, no camera bumps, and a design that shows personality. Since the 6, they are still perfectionist, good looking phones, but a bit bland, imho. to bring out the old car analogy: the 4-5s were deloreans, the 6 is a tesla model 3 - curves, but no edges.