The things I like the most in XR:
the atmosphere,
the art direction,
the ships design,
the stations design,
the economy that I find more involved/interesting to solve,
the specialist workers,
the manned drones,
the diversity of missions,
the procedural stations interior,
the interaction with all the NPC,
the scope of the universe (not too big),
the dogfight feels better to me,
Proud of Albion is the perfect ship for me to fly, she's fast, nimble, sturdy and powerful enough to go one to one against a Xenon I or a Fulmekron.
etc.
I don't find these things in X4...to me X4 is full of wide and big empty generic spaces with some boring modular stations here and there which look all the same.
X4 is the true X3 sequel, a space economic simulation.
X Rebirth is a new brand, with new gameplay and mechanics I'd like to see Egosoft build upon it.
XR is more like GTA in space, it feels more like a space RPG with a little bit of empire building.
XR2 could evolved to full Space RPG, with more stories, NPC interactions, like Skyrim in the X universe.
I know I have big dreams
Bethesda is working on Starfield, maybe that future game will be what I'm looking for...