Finally got some time to navigate all the menu and do some quick tests. Call me impressed.
Surprise one: one little old desire (that nobody mentioned in the reviews) was that now the "3d" electronic level could be enabled pemanentely on the screen / EVF; in the X-S10 - and I guess in all the last generation's Fujis - only the horizontal level was permanent, the 3D version should be activated by a custom button, and disappeared after taking a shot.
Surprise two: a new focus assist tool, only in video mode - Focus Meter. Is a "needle gauge" that shows where to turn the focus ring to bring the image in focus, and that could be used in conjunction with peaking. Works very well and very accurately.
And finally, the AF. The face / eye AF interface and working mode was completely changed form the 4th gen Fuji's. In these (X-S10, X-T4, etc), when face / eye AF is on, the camera selects a face / eye and shows it on the screen in green, the other faces are marked with grey boxes, and you could change the face to focus with the joystick. In theory, a good system - until you hit record, and the camera goes haywire changing the face focused at will. For me, with more than one face on the frame, was unusable.
Now, you choose a area box (that you could resize), and the camera will focus on the closest face of the box. Period. And tends to stick quite a bit in that face before switching to other. Not a perfect system - did not tested the worst situation, with all other people standing in place and the focused person going to the edge of the frame, far from the box, which in theory will make the camera changing the face focused - but if you keep the subject in the same spot of the frame, or move the box with the joystick, works perfectly.
There are more subtleties to discover - one test was filming my wife's father, my wife and my daughter playing in our living room, tracking my daughter (an electric 4 year old), a case which the X-S10 failed completely; the focus point moved from person to person if they are close. With the X-S20, started tracking my daughter, and NEVER let her go. Focus spot on 100% of the time. And with an unexpected behaviour when my daughter got very close to my wife's father, instead of jumping faces, the old gray box appeared on his face, but the AF was kept on my daughter. One touch on the joystick, and then he was in focus - even with my daughter closer to the AF box. Another touch, returned to my daughter. Just as I wanted to be.
The detection is much improved too. In the X-S10, if the person turns and the face did not appear, the camera reverts to the original AF mode. The X-S20 recognizes the back of a head - when the person turns, it starts tracking the back of the head. The person turns back, it revert to the eyes again. And the face / eye detection works in much farther distances than before, and gathers eye / face instantly.
Is a completely new behaviour, much, much better than before.