It also feels impressively classy. The way the door thunks shut with satisfying solidity, or the way the window scrolls down slowly at first to allow you more easily to stop it precisely, speaks of painstaking build quality and even more painstaking thought processes behind the making of this car.
The diesel engine fires up with an audible but far-away grumble and step-off is smooth if a bit lazy, bleeding into a power delivery that doesn't suffer from overly bothersome lag despite the D4 not getting the PowerPulse air compressor that the D5 has to reduce its turbo lag. What with the standard eight-speed auto - also smooth and a bit lazy - blurring shifts so well, the S90 D4 is perfectly suited to surfing around on its more than adequate torque band, enjoying suitably boss-like acceleration and overtaking when you want it and just settling to a fairly charming mooch the rest of the time.
Maybe we'd like the engine to be a touch less gruff when you do go for harder progress, but the D4 is one of the quieter engines in the class on a steady throttle. Tyre noise is more likely to intrude on your consciousness, especially over coarse surfaces, but even that's easily ignored.
Our car came with optional £950 adaptive rear air suspension and rode on 18in alloys, which gave it a pillowy ride comfort much of the time but did come at the cost of quite wallowy, long-wave body movements that some might find a touch off-putting. Even over fairly smooth road surfaces there's a sense of the car floating about quite a bit, so it comes as no surprise that - even in Dynamic mode - there's quite loose body roll when you weave through direction changes.
That ride comfort isn't infallible, either. Hit a mid-corner pothole and the suspension rebounds quite jarringly, although the rest of the time you rarely feel more than a mild shiver even over poor surfaces.
Inevitably, the soft suspension doesn't lend itself to particularly precise, incisive handling, but the steering is at least hefty and predictably geared enough that you've got the confidence to make the most of the decent grip levels. So don't worry; there is still real satisfaction to be had in threading the S90 down a B-road. It's not a sloppy mess by any stretch, just a bit softer and more roly-poly than the likes of the keener-feeling BMW 520d. In among all this, it's worth clarifying that the S90 is a stand-out motorway cruiser. It tracks straight and true with little effort on your part, and between that directional stability, very decent overall refinement and even the standard 'Pilot Assist', which is in effect a very advanced combination of adaptive cruise and lane-keep assist, this will do the long-distance haul with serious style and serenity.
There's little to criticise in the S90's cabin. The driving position from the broad, cushy seat is very good and offers decent breadth of adjustment, visibility all-round is good, the dash is mostly easy to fathom, the screen easy to see and one of the easier systems to get used to and there's masses of space in the back seats and a really sizeable boot. You even get 60/40 split folding rear seats as standard, which many rivals don't offer.