Bumping a zombie thread. But as a former 23 ST owner(purchased new) and now a 25 ST owner(purchased new), I can give some opinion on this matter. The biggest notable improvements with the 25 are all in the interior. The interior sounds and feels completely different. The new design is more spacious. The leather/suede* seats are more comfortable. The wireless phone charger works with large phones now because it sits flat on a wide shelf. The layout of the integrated sound bar style speakers in the dash sound more immersive. I personally am experiencing A LOT less engine/wastegate knocking noise from inside the cabin. Perhaps Ford listened and reduced the FENG a little bit. Or maybe the new interior design insulates better, but my 25 is much quieter inside in normal driving mode. Ford literally said that they redesigned the interior to simulate the comfort of a living room.
From a technology standpoint, the 20-24's don't even compare. For starters, the infotainment system is vastly improved. The 13.2" horizontal layout on the 25 provides a better full screen appearance. Apple Carplay/AndroidAuto) is wireless now and connects the moment you press the Start button. The responsiveness of the system is extremely fast, there is enough CPU power to play video games(one is included). You can watch full screen Youtube, when parked with the included app or add other video apps. BlueCruise was added, and although I will rarely use it, it's pretty neat to sit back and let the vehicle drive itself on the highway. The dash now has a tachometer in normal drive mode without a bright blue background, and Ford also added some temp gauges to the menu which you can toggle on if you want to monitor them.
There are many improvements which elude me right now, but to be fair, I'll mention some things I miss from my 23. The biggest issue I have is no physical HVAC controls. It took some time to get used to using the touch screen to control the A/C. The different drive modes have different animations, but they all share the same screen layout on the dash. I miss the variety of screens. My 25 is a Job 2 build, so I don't have the retractable sunshades in the rear passenger doors.
As far as QC goes, it feels similar, it's a Ford. My 25 is definitely quieter inside, but as time goes by, I fully expect it to develop the usual rattles and creaking plastic noises. But maybe I'll get lucky.
*The comfort of the seats is obviously subjective, and I know they aren't real leather/suede.