Seems I've been sent a faulty Scorpio Edition by Amazon.
When I first powered it up it took an age to get into the dashboard (5 minutes).
When I began the games transfer over wireless from my One S the game transfers failed one after another. Some copied half the file (15GB etc.) before failing. I kept manually restarting the transfer, but it just failed, over and over again. In the end I cancelled the multiple games transfer and did the ones I really cared about individually. This worked but the transfers took ages (Halo Collection took 2 hour, for example).
I installed Forza 7 and the Xbox One X performed a download simultaneously. By the way, I have 200mbps fibre with Xbox One X getting 166mbps download on test. Installation was incredibly slow. After 2 hours the update download was at 82% and it said I could start the game, so I did. The games screens were a bit jumpy and loading was S-L-O-W. I played for a few mins and completed the first 3 challenges that introduce you to the game. I then went to the Home screen to see if the download had finished. First I saw the download tile showed the same 82% downloaded, then it disappeared. I figured it must have finished and the report of 82% had been a glitch, but when I went to my Games and Apps page Forza 7 game tile had vanished too! Literally. I had to restart the Xbox One X and reinstall and download the game all over again. My Forza 7 auto save file had vanished too as I had to start from scratch.
Then I tried to play Rayman Legends (360 game) and it took 1-2 minutes to get passed the first 'holding' screen before the emulation began and the 360 swirly intro appeared on screen. Later attempts didn't have the same issue and the 'holding' screen (a picture of Rayman and Friends swimming) was only shown for a few seconds.
Other screens have sometimes hung as well, or taken ages to be replaced by the next screen. Other times they are fast.
The next day I turned the Xbox One X on and the dashboard screen appeared but with ZERO content. After 2-3 minutes the screen went black and then the dashboard reappeared with all my stuff on display.
Randomly the Scorpio Xbox One X will be slow to do something. Often it's slow to start up, sign me in and display the dashboard when its been turned off on the wall socket, but sometimes its slow after being started without having been turned off on the wall socket.
Some screens behave funny too. I sometimes see isolated flickering, noise artefacts and lighting oddities. I'm not sure if this is the Xbox One X or my tv though. When I first used the XBOx One X I had to spend an hour testing and setting up the TV's deep and complicated picture settings to get a non-juddering and blur free image. Local dimming on my LG 60" 4K HDR isn't the best and I think that causes some of the light oddities even after all the settings changes. So, I'm not blaming the Xbox One X for image issues necessarily.
So that's been some of my experience with the X so far. Amazon say they can refund but can't replace as the Scorpio is no longer available. I haven't contacted Microsoft yet. I may do that next. It's annoying as it sometimes works fine, but other times performs badly.