If you are planning to upgrade to iphone 6s from 5s or earlier it made worth the upgrade.
But if you already bought the iphone6 last year please drop the Idea as soon as possible because honestly its not much different than the last one.
Sure the cameras are better, photos can come alive and the 3D touch lets you access shortcuts and new menu options for your apps. But these features have minimal impact.
Camera: More pixels are added to both the sides, which can capture more details in your pictures. but you wont notice much of the difference in photo quality.
Live photos: I am not a huge photo-taker, but I love that I can swipe these photos to see moments to play out before and after each shot was taken.
3D touch: Despite being pretty niffty trick, 3D touch is not all that useful yet. most apps dont work with 3D touch. For those who support 3D Touch, thise work quite well.
Using iPhone 6S feels no different than using iPhone6.
The durability has increased with new kind of Aluminium. The TouchID is much faster bu thte animations make it slower to open up the device as usual.
Upgrade only if hadnt bought the iPhone 6 last year.