I've only done 215 miles so far and this is the first ZX I've had so cannot compare to previous models, but I think I've seen just about every youtube vid on all models
The big concerns for me were smoothness of the throttle mapping, turn in and vibrations.
I've heard reports that the mirrors can vibrate around 4k RPM and effect the clarity, I can honestly say that so far, with a quick run to 6K I ha vent seen any issues.
There is a tiny amount of vibration at 4K RPM in the pegs and grips (and pillion pegs apparently) but I would say it's very slight, by 4.5K it's clearing up. I would say I'm quite sensitive to vibration but this really doesn't bother me, it's way better than my 2016 MT-09 Tracer.
Throttle mapping is excellent, I have no complaints at all. You can ride very smoothly at very low speeds, however the ability to tweak the engine breaking would be nice.
Throttle response is fantastic and instant even in 6th at 30MPH.
KQS is nice, and makes riding with pillion smoother and a bit of fun when solo. Gear lever does feel a little "spongy" on the down shift as a result but doesn't seem to cause any issues with finding neutral.
Haven't played with the suspension as it seems nice and plush from factory for both solo and pillion.
I get a numb bum after 1.5-2 hours of riding *However* I have the Ergo low seat as I'm a short arse so I cannot comment on the seat as supplied. My wife says her bums had enough on the new comfort pillion seat after the same amount of time though.
Turn in and handling is exactly what I wanted, smooth, predictable, easy and stable...very stable.
Love it and have no regrets or complaits about it, it's exactly what I hoped it would be