So is it worth an upgrade?
All told, outside of the upgrade to a new processor and a better camera, the main feature of the new iPhone 6S and 6S Plus is 3D Touch. And while the new pressure-sensitive interactions are certainly intriguing, they may not scream out as an immediate "must have" for some users.
One complication to consider is that no matter how useful 3D Touch proves to be, Apple has to deal with the fact that they are essentially hiding menu options throughout iOS. This is inevitably going to result in a bit of retraining for users, who will have to build up muscle memory and overcome everything they've already learned about interacting with a touchscreen just to take full advantage of 3D Touch.
If you're due for an upgrade, or simply love the experience of being an early adopter, there's no real reason to forego the new iPhones. You'll be getting a head start on adjusting to 3D Touch, and you'll also get to take advantage of the iPhone's increased camera prowess and speedy processor. If, however, you're skeptical of 3D Touch's uses, it may be worth waiting another year for the inevitable kinks to be worked out and widespread developer support to arrive.
- Read our hands-on with the iPhone 6S