Besides the difference in dimensions, in display sizes, and overall design, the iPhone 6s and 6s Plus also come with an impressive camera, light years away from what Apple managed to add into their first generation iPhone model.
If you never owned a 1st gen iPhone, or you don't know already, Apple's first iPhone came with a 2-megapixel camera, capable of capturing 1600 x 1200 pixels photos.
This compares to iPhone 6s' 12-megapixel camera, which comes with a dual-LED (dual tone) flash and phase detection auto-focus, allowing the user to snap 4608 x 2592 pixels HDR photos.
Furthermore, the camera available with the iPhone 6s is also capable of automatically geo-tagging your snapshots, to help you focus with a simple touch on the screen and to record 4k videos, that can also be recorded in slow-motion.
To make matters worse for the first iPhone model released, the second camera of the iPhone 6s is better than the one in the iPhone 1st gen
To make the difference between the iPhone 1st gen and the iPhone 6s even more obvious, the iPhone 6s also comes with a second 5-megapixel with face detection and video recording just like the one on the back, a better camera than the main and single one available in the original iPhone.
Just in case you need any help visualizing how far apart the first iPhone and the iPhone 6s and 6s Plus are from each other when considering the changes in camera alone, I attached an infographic below to help you get an overview of how much Apple has changed its iPhones since the first one was released until now.
The infographic was created by Lynda.com and it details the camera specs for every iPhone released by Apple since 2007 until now.