* topological naming issue mitigations -- this is mostly solved enough that you can rely on it, though there are definitely still times when it makes more sense to use sketches offset from the base planes
* the new integrated Assembly workbench (and solver) though I've not dabbled with this myself
* really significant improvements in the sketcher (easier dimensioning, curved slots, polar arrays and improvements to the array tools controls, offset/scale, automatic midpoint constraints)
* support for bodies with multiple non-overlapping solids in Part Design
* useful subtle improvements to Part Design array tools
* some support for operations (pads/revolves/pockets) on only selected shapes from a sketch in Part Design
* I don't do CNC yet but I think there are improvements in the CNC workbench that would benefit hobbyists.
I would put the UI improvements somewhere lower down the list, frankly, than they do, because I find them often confusing and regularly frustrating on laptop screens, but:
* the new dark theme is really nice
* OpenTheme's dark theme works well
* quick transparency toggling is helpful
* and the optional tab bar for workbench switching helps make various disparate workbench tools just that much quicker to get to, somehow, making it all feel a little closer-knit