The design doesn't bother me.
Sure, I understand how people want some kind of radical new design but in general the 6 series, although somewhat bland and approaching the two-year-old mark, isn't awful.
In comparison, the iPhone 4 and 5 series are a very similar design to each other and that design survived four cycles.
OK so, the 5 did have a particular design update with the accommodation of the taller screen, exterior coloring, and was also slightly thinner, but overall they were very similar, design-wise.
On that note, the 6 design is only at its third cycle in comparison, although with subtler changes.
Considering how popular the iPhone SE is - simply changing the design for the sake of it doesn't always matter.
The SE is a very capable phone and people love that design - it's considered a 'classic' now.
As far as smartphones go - the designs of all of the leading current models are really very similar when you think about it - reasonably thin, a screen, a couple of side buttons, a home button and a camera hole. It's hard to tell many of them apart from a distance, especially since so many people use cases. The Samsung Galaxy Edge with its arguably gimmicky side screen probably the exception as far as design goes.
Sure, maybe it's Apple's prerogative to come up with the 'best' aesthetic design but what I'm really interested in is what is under the hood.
I'm wanting the best possible camera I can get in an iPhone - looks like the iPhone 7 might deliver that. We'll have to see.
I spend more time looking at the screen of my phone to take and edit photos than I do admiring its physical look, turning it over to look at the back of it...
So yeah - I'm not worried about they way this looks.
Besides the phones usually look way better in the flesh and I always use a case which covers up the back so...