I have the same problem with my iPhone 6s Plus. Photos looks washed out and lost many small details (small branches on trees, grass, facial features) and objects lost their textures (like bricks or concreet pattern). Before this phone I use iPhone 5 and the photographs where significlly better.
Same locations shoot on the same day on iP 6sPlus an iP 5
http://imgur.com/a/Md4f7
It looks like denoise and sharpening filter been used (as many of you have mentioned). I've go an old Fujifilm camera with the same problem - denoise filder remove small details and the artifacts on images looks the same.
iPhone 6s Plus photos have no or very little chrominance noise compared to iPhone 5 even on lo ISO but the details of images are lost. Color representation/ whote balance and image stabilisation on iPhone 6s is significally (sometimes drmatically) better than on iPhone 5. But at cost of reduced details it is not good.
Most of the people dont see any difference with iP6sP pictures. They are very pleasant especially when viewd on small screeen or resampled to lower resolution. They tend to see nois and hate it, but if there is no noise - there is no details 🙂
I don't think Apple will chandge camera behavior because most of the users will complaion about noise, but I still hope for an option to disable noise reduction for "power users" hidden somewhere deep inside settings app or an option to keep original (noised) photo along with processed photo similiar to HDR.
