My old man recently acquired a 99 Z3M with the S52 and can give a reasonable comparison. Bone stock outside a cone filter, and KC line coilovers. They drive and feel completely different. Z has period steering weight and on center input is much slower to react. S52 is down on power compared to S54 but is arguably a much more stout engine to beat on. Lots of torque and enough power to have fun, makes a proper noise the last 1500rpm of rev range.
Shifter is...vague to say the least especially compared to the FRS/BRZ. Shifting into 3rd gear is like neo and his spoon; you need to believe third gear is there when you shift into that area and know it'll go in. The first time I drove it I spent the entire drive trying to nail third and shifted 2nd to 5th several times.
Edit; I forgot to mention seating position or rather the seats. They're more relaxed fit and find them slightly awkward. The clutch pedal is long, longer than it needs to be. It has a longer engagement point and more dead zone. Getting into the 86 after driving the Z makes clutch on the 86 feel like a button
Overall it's a fun car, but for entirely different reasons. When I drive it I want much more wanting to cruise and hear the engine than drive the nuts off it and hunt for a corner to attack. Perhaps some adjustments could remedy that, new tires are in the works for next year and I may try to fiddle with the coilovers to see how where they're adjusted too.
