I have seen very few user comments on the T6s so I thought I would add a few. If anyone is interested I would be happy to provide more followup at a later date. I just received my camera and 18-135 kit lens today.
I am upgrading from a T3i. I have a lot of miles on my T3i. My XSi died after heavy use due to shutter failure. That happened in one of the most remote parts of the US. Rather than face that with the T3i, I decided to retire it and keep it for a backup camera.
I also wanted improved image quality. I do most my printing at 16"x24" so the jump from 18 to 24 mp gives me a modest improvement with a corresponding jump from the equivalent of 216 dpi to 250 dpi. I also hope to see somewhat better image quality due to improved noise reduction and even some improvements in dynamic range. I will do some of my own studies but I am sure my comparisons will not be as detailed as the comparisons from experts with laboratory resources.
I was also hoping for improved AF performance. The T3i has been lacking and I miss a lot of action shots due to poor focusing. In addition I do a lot of macro photography and the T3i AF has been horrid for macro work. I can start by saying that I am very happy with the T6s AF. The focusing seems very fast and accurate. I checked for front and back focusing and the camera seems to focus spot on. I also did some tests for the standard viewfinder focusing and compared the results to manual focusing with liveview at 10x magnification. The AF results are consistently very close to the 10x manual results. In addition I tried my 60macro at the closest possible distance and the AF worked great. I played around for several minutes and had no AF failures compared with my T3i that will not AF closer than about 1:2 or 1:3 macro.
I did an out of focus sensor test at f/25. The sensor looked clean with only one small spot on one edge of the sensor.
I noticed the DPR review commented negatively about the placement of the lower selection wheel. Maybe I don't know any better due to lack of experience but I have no issues and this definitely made some adjustments more convenient. I have also read negative comments about the viewfinder magnification. This dropped from 0.85x to 0.82x. I could not see this difference when comparing my T3i to the T6s. The T6s viewfinder actually seemed to be a bit brighter.
This is my first camera with an electronic level. I was very happy with it. It will be especially useful for photographing waterfalls. I no longer need the old bubble level.
I am also very happy with the lock on the mode dial. I have had the mode dial move accidently many times when removing the camera from the case for when trying to shoot with winter gloves on. Unfortunately the Off/On/Movie switch is annoying. I kept hitting movie mode when trying to turn on the camera.
I have one other negative about the T6s. It feels like it is made of cheap plastic. I looked at my T3i again and it seems to be made of the same materials but somehow feels better. Maybe the feel will improve with some dirty fingerprints and a few thousand hours of use.