IPhone 6s is a huge improvement over its predecessor iPhone 6. It has removed all of the shortcomings of iPhone 6.
A much improved in hardware with its A9 CPU, new PowerVR GPU and an attractive 3D touch makes it unique.
Camera is improved as well with its OIS and the build quality is also solid.
Things to like about this Phone(Pros):-
Build Quality of Phone is great. It is much more durable compared to iPhone 6 and you wont be able to bend it easily.
It comes with Dual Core A9 CPU clocked at 1.8 GHz with 2 GB of RAM and has GTX 7600 PowerVR GPU. Everyone might thinks that 2 GB isnt enough but ios 9 utilizes the hardware in a very optimized way so that you wont feel any problem in gaming and multitasking.
it comes with ios 9 out of the box and upgradable ios 9.2.
It has IPS grade screen with resolution 750*1334(326 PPI) which gives you sharp image quality and great viewing angles.
It has the best iPhone camera ever. 12 MP shoots very well sharp images. Low light photography is well. now it can support 4K recording. OIS does a great job while recording video.
Display has introduced a new 3D feature which is quite new, live images is introduced which does a good job.
Things to not like abut this phone:-
It has NFC but only restricted to Apple pay.
It is a flagship device but has only HD equivalent screen where other vendors are providing a 2k screen and even 4K screen.
Camera is good but not the best among every other phones.
16 GB model isnt future proof if you soot 4K video regularly. 64 GB is sweet-spot but priced insanely high.
live images is nothing new concept which you will find on every Windows phone.
Conclusion:-
If you are Apple fan using iPhone 5S and looking for upgrade then Id recommend this phone. iPhone 6 user might opt for this phone as well. People should go for 64 GB variant.
iPhone 6 was like, see we can make big phones too but there was nothing special about it.
iPhone 6S provides lots of new feature as discussed above and with 3D Touch and Live images you will feel great.