The 4 series exudes quality and presence. It's timeless masterpiece far beyond anything other mobile device makers have ever offered. Alas, it also had the signature Ive/Jobs touch: a sacrifice of function at the alter of design.
The 5 series to me always seemed like a cheap aluminum version of the steel and glass of the 4 series. It was the first iPhone to feature bend reports, albiet not as ubiquitous as those for the 6+.
The 6 is very nice, even pretty. A bit elegant from certain angles. Yet somehow it lacks the je ne sais quoi that made the 4 series such a timeless work of art. It's almost, but not quite, boring. The protruding camera is almost, but not quite, ugly. The antenna bands almost, but not quite, blend into the aluminum chassis. It feels almost too light in the hand, and yes it is as flimsy as it seems. A missed opportunity since properly engineered steel reinforcement could have put it in that rarified domain of objects that are thin and slight yet rugged and strong.
The iPhone 6 is Ive's solo project that begs for Steve Jobs's aesthetic guidance. I think that's what bugs me about it most: it reminds me that Jobs is gone for good.