I'm not exactly how the new vehicle is a 'huge let down'.
Nope, I don't have one yet, but from various reviews I've seen:
The car is quicker/faster than he previous version in just about every way (More power/torque/etc.)
The interior has been upgraded with better sound proofing
The suspension is apparently substantially better
Slightly improved aerodynamics
Ventilated sports seats
Slightly larger front screen
Addition of the rear-seat screen
Fewer parts = fewer potential points of failure
And so on.
Is there some definitive/measurable way in which the new M3P is 'worse' than the previous year?
Not trying to be argumentative, just really trying to understand some of the disappointment I see. So far it seems like it boils down to some folks having high expectations, and when high expectations are not met, even smaller improvements are often overlooked.