That's not to say it's useless, because entering corners at speed reveals decent grip, and, as long as you have the suspension in its Sport setting (one of three), a surprisingly well-behaved body.
The problems lie with the steering. It's a heavy car, this, and it feels it when trying to tuck the nose in to bends, while the steering never really weights up enough to give you confidence. The lack of feedback is almost a given.
Switching the chassis to AMG's Dynamic Curve mode actually helps lean the car into bends before you reach them, but the end goal isn't greater cornering speed, says Mercedes, it's enhanced comfort. It works reasonably well, helping to quell some of the pendulum effect this two tonne Mercedes suffers through fast chicanes.
That said, even when dialled right back to Comfort mode, the S65 picks up on rivets and broken Tarmac a little more readily on its standard 20in wheels than the lesser S-Class Coupes, and certainly more than an S-Class saloon. Mercedes' impressive Magic Ride system seemed to miss more approaching speed bumps than with the saloon, too.
The S65's power delivery is more suited to GT continent-crossing than precision back-road blasts, too. Stamp on the throttle from stationary with the traction control switched on and it's a case of computer says no, as it tries desperately to divvy up the huge amount of power and torque. The result is squirming and dithering for the first second or two before the power is put down.
Of course, switch the traction control off, and the rear wheels will spin until their tyres flail away. No, where the S65 is best is from a rolling starting. On the motorway, you can simply pick a car on the horizon, squeeze the throttle and fully expect to be overtaking it before you've chosen which type of massage you like from the driver's seat. Also to be expected is around 15mpg.
Indeed, if the S65's performance is staggering, its cabin isn't far behind for wow factor. Its quality is some of the best you'll see anywhere, and the standard front seats are some of the most comfortable and adjustable it's possible to sit in. They'll heat you, cool you, focus on massaging your shoulders or your lower back if you so wish.
Two large 12.3in colour screens sit side-by-side on the dash, displaying the instruments on the right and infotainment on the left. They're beautifully bright and crisp, and controlling the endless features using Mercedes COMAND rotary dial between the front seats is simple enough, even if the system's menus aren't the most straight forward on the market.
There's enough leg room adjustment in the front seats to free up some rear seat knee room, but if the front passengers are over six foot, then it'll be an uncomfortable journey for those in the back. The boot is better, offering 400-litres of space and surprisingly decent access given the Coupe's sleek lines.
S65 buyers can expect those larger 20in alloy wheels, S65-specific front bumper styling, an AMG sports exhaust, LED headlights with Swarovski crystals, an interior swathed in Nappa leather and an upgraded Burmester sound system in return for braving the considerable financial step.