“ISOLATED” is a word that best applies to our A6 2.0 TDI drive on South Australia’s Kangaroo Island last week, since it refers to both the environment and the car.

As Australia’s third-largest island, it features flat, scrubland permeated by smooth if undulating straight roads with little variation.

For the vast number of potential A6 buyers, this geography does not apply to their usual driving route.

So on these lonely and unique roads, the A6 2.0 TDI Multitronic (the only version we managed to drive, although there were 2.7 TDI Multitronic models also at our disposal) felt smooth, quiet, and amply powerful.

The 125kW/350Nm 2.0-litre four-pot TDI is one of the best diesels of its size around, providing creamy refinement and a surprising amount of punch from low revs.

In its A6 2.0 TDI application, a CVT Multitronic is the only gearbox available, driving the front wheels with seamless ease.

However, acceleration is languid from step off, while there is not much overtaking urge in the upper ranges. This should come as no shock, since the Audi tips the scales at a portly 1660kg.

Unfortunately, despite the wholesale improvements made to the A6’s steering and suspension systems with the MY09 Series II facelift, this car is an anodyne driving experience, with light but dead-feeling steering and a suspension set-up that is still a tad too busy and firm for our liking.

At least there is plenty of space in this large sedan, with ample room for legs, heads and shoulders, and a big boot to match. And little disturbance comes in from the road or wind on the smooth and, yes, isolated Kangaroo Island roads.

But in base-level trim, the dash – though expertly designed and beautifully made – is beginning to feel a little dated, especially compared to A6’s A4 baby brother.

In fact, it is the Audi’s newer sibling that undermines the A6 2.0 TDI’s place in the world.

In isolation, yes, the latest addition to the A6 range feels adequately powerful and sufficiently nice to drive, but the A4 – almost as large now and a whole lot more interesting as well as better to drive – is a better overall package.

You can save at least $20,000 and have the superior vehicle in the A4 2.0 TDI Multitronic, or spend $10,000 less and enjoy the treacly urge of the A4 2.7 TDI V6 Multitronic, or spend $10,000 more on the all-wheel drive A4 3.0 TDI quattro and revel in its effortlessly strong performance and unparalleled 4WD grip.

Knowing that the A6’s C7 replacement is probably just two years away while the current A4 will stick around for a whole lot longer is another A6 drawback, no matter how keenly priced the 2.0 TDI is.

That the all-new Mercedes E-class is here, and a redesigned BMW 5 Series not that far away, means that the A6 is now an isolated last out of the triumvirate of mid-to-large German luxury cars.