The camera has gotten much better. Daylight performance is great, and in many occasions better than the iPhone's. Low light performance is good, especially if you use manual mode or RAW. I returned to the M9, because the 5.1 corrected all issues I originally had with the device:
- Camera is really good
- The slow charging issue has been solved
- There is an option to change the color calibration of the display. Before the update colors were very cool. I like cooler colors, but this was really extreme.
- Android 5.1 provided performance and battery improvements.
All in all, I love my M9, despite HTC's bad marketing. The overall experience is great. People unfortunately judge mostly very poorly and look only on the surface of things. I wish HTC a fast recovery and hope that we will see many great devices from them in the future.
The other reason I returned to my M9 and sold my iPhone 6 was, that the new iPhone 6S won't have anything that will make me feel excited about. Better CPU, same display, better camera and force touch..This is not enough.