In a literal sense a driver’s car is merely one that can be driven by anyone who has the ability to drive.
But in the sometimes overused Autocar sense of the term, a driver’s car is one that we feel is unusual in the satisfaction it delivers to the person behind the wheel.
Which means any judgment we may make in this context is always going to be subjective, rather than objective. It’s what we as a collection of individuals feel about a car, not something we can prove or justify via scientific measurement, and it’s important to understand this whenever we refer to a driver’s car – past, present or future.
As to what constitutes a driver’s car, several key factors must be present in my opinion, most of which are again subjective judgments in themselves.
It must have good steering feel (which is entirely subjective), it must have an approachable, natural sense of balance to its handling (ditto), a well resolved, well damped ride (ditto), it must sound good (ditto), it must have good clean throttle response, a decent gearchange – be that manual or paddle-shift – and seats whose springing is in sync with that of the chassis.