@david_ten
I don't really know how to describe it without sounding like the sort of religious zealot that people who advocate for these things are stereotyped as.
Using general terms, I'd say detail and focus are most impacted. Things are more realistic and engaging. (I know that sounds insane.) In my system, the difference was not subtle. Sounds became holographic. People have complemented my "center channel" despite there clearly not being one.
I would consider buying more (and upgrading the ones I have), but despite my enthusiastic patronage, I'd hesitate to recommend them. The only thing stopping me from buying more is budgetary constraints, but if I had none, there's nothing else I would buy. I'm happy with my components, cabling, speakers, and room. I'd get the newest ESS Rack, Ultra 5s under my speakers, Ultra 6s on grids for each of my components, and a dozen more aperture panels.
Then I'd be *done*.