During my Taipei trip, I had the opportunity to extensively use the iPhone X's camera, and the verdict is this: it's utterly fantastic.
It's amazing what camera lens can do when it's paired with incredible computing power. Apple overcomes the physical limitations of the smartphone form-factor - sensor and lens can only be so big - by performing calculations and predictive algorithms that traditional camera makers like Canon or Nikon cannot. The iPhone may be outputting JPEGs, but those photos have got vastly more computing done to it than say a Canon 5D - and all the user do is press the shutter, adjusting nothing.
I got astounding hit-rate with the iPhone X JPEGs on the trip: exposure and color temperature are almost always spot-on.
Of course, Apple have upgraded the sensor technology as well, but I firmly believe it's the A series chip inside the modern iPhone that's the X factor in the tremendous photo capabilities. We're to the point where my non-photography inclined friends cannot discern the difference between - when viewed on mobile - the shots off of the iPhone X and A7R2. With the iOS 'portrait mode' in its second generation, the X can even do convincing bokeh shots. It's truly astounding.
In the future I would have zero qualms about leaving the dedicated camera behind and simply use the iPhone X as the sole travel camera: it is that good. Once Apple figure out/allow proper long exposure shots, there will remain nothing an iPhone can't do that a proper camera can. Even dynamic range limitations are already solved by iPhone's brilliant auto-HDR function.
From a photographic perspective, a hearty job well done on the iPhone X, Apple.