I have been using the Mate 9 for about 10 days and wanted to post my thoughts. I tried to wait a few days because I often like a phone a lot while setting it up, only to find faults after using the phone a few days. I have used about every one of the top phones on the market (iPhone 7+, Pixel XL, S7 Edge, 6P, LG G5 and V20, HTC 10, Moto Z, One+3, Axon 7, etc.) and this is the best phone on the market right now, in my opinion. It has the best combination of size, screen, software, battery life and camera.
Screen quality is always very important to me and I returned a number of phones because I could not stand the screen (LG I am looking at you). I was concerned about the 1080p, relatively low pixel density LCD screen, particularly considering the big 5.9 inch screen. In fact, I initially dismissed the thought of getting the Mate 9 for that reason. However, the screen is great. I can put it up next to the Pixel XL and look at the exact same things (pictures on 500 px, games, various apps) and rarely do I notice the difference between it and the AMOLED screen. It is much better than the smaller 1080p screens on the 7+, One+3, etc. I don't know how Huawei did it, but the screen is impressive considering the specs.
The battery is awesome. The software with Nougat flies. It has a much larger screen in the same size body as the iPhone 7+ and the Pixel XL. Connectivity has been good (bluetooth works better than the Pixel). It works well on AT&T -- of course HD Voice is not available. I have not taken many pictures yet, so I cannot really comment on the camera.
I have a hard time finding fault with this phone. Hopefully, Huawei will support it and issue quick security and other (7.1.1) updates.