MERCEDES-BENZ pioneered the prestige SUV market with the original chassis-based M-class back in 1998, and were soon joined by a raft of softer and more urban-friendly rivals that won buyer approval.

As the BMW X5 in particular slashed into the market after its launch in 2003, Benz inevitably caved in with the second-generation model that arrived in 2005 with a more car-like unitary construction in place of the previous ladder-frame system employed by serious off-roaders like the Toyota Landcruiser.

Clearly, buyers of premium SUVs were not inclined to take their expensive machines deep into the wilderness, but they paid the price of such ability with the original M-class in the form of compromised ride, handling and noise where they spent most of their time – on the bitumen.

On its release, the second-generation M-class matched all its rivals in those critical areas, and also gained points in the fuel economy department as a result of pruning weight, despite growing considerably in size.

Sales almost doubled and rocketed the M-class ahead of the Volvo XC90 and Jeep Grand Cherokee, but it was still not enough to regain market leadership from the X5, or even second place from the Lexus RX330.

With the mid-life facelift on the cards following the publication of photos in March, the M-class lost quite a bit of ground this year, dropping into Land Rover Discovery, Range Rover Sport and Audi Q7 territory, but Mercedes-Benz Australia anticipates that its arrival will restore the status quo.

Electing to keep the existing mechanical package, including the same five engine variants as before, the new M-class is very much a facelift in the true sense of the word, with most of the changes being cosmetic.

But this is no bad thing because, as previously outlined, the second-generation machine is already very impressive on the open road while still having the capability of going off-road to perhaps a greater degree than most of its premium SUV rivals.

The ML320 CDI that we drove on the national media launch displays all the strengths of the range and underlines why diesels now account for more than 50 per cent of Mercedes’ SUV sales.

It started instantly, pulled away strongly and displayed little of the engine clatter – at least from inside the vehicle – that once marked diesels, and of course will return much better fuel economy than any petrol-engined version with similar performance. In fact, the 165kW/510Nm 3.0-litre V6 engine returns the same consumption figure (9.6L/100km) as the less powerful (even though it is the same size) 140kW/440Nm version in the M280 CDI.

With the ML320 priced just $3000 above the V6 petrol ML350, which cannot match it on economy, it is little wonder that buyers are turning to the modern piezo-injected turbo-diesel option. With a 2.1L/100km advantage, the CDI buyer would make up the difference in 100,000km while enjoying better real-world performance and lower emissions in the meantime.

On a varied range of country roads, the M-class sat firmly and flat on the road while absorbing some harsh bumps (even with the bigger wheels), making it a more than capable cruiser, and the new seats proved to be very comfortable and supportive over the distance.

We do not mind the steering column-mounted shifter for the slick seven-speed auto, but if you want to self-shift at any stage you have to make do with the steering wheel paddles rather the Mercedes’ usual user-friendly side-to-side centre shift.

The changes to the interior are relatively minor, but the exterior revisions certainly give the M-class a tougher, more AMG-like look with the louvred grille, step-down headlights and changes to the rear that make it look less upright than before.

Once again, about the only negative with the M-class is the standard fitment of a space-saver spare tyre, which is something we think is particularly inappropriate for a vehicle that has the capacity to be taken off-road, and for which quite a bit of technology is included in the vehicle.

However, we have to give Mercedes-Benz credit for again offering two options for those wanting an uncompromised spare – a raised cargo floor to accommodate a wider full-size spare in the original position, or a separate rack that fits on the back of the vehicle to carry a second (full-size) spare. But both dealer-fitted options are costly, being priced at around $2700 for the floor conversion and $4500 for the back-door unit.

That is not a minor quibble, but certainly a rare one in the case of the M-class.

We are not fans of luxury SUVs that don't go off-road, let alone ones weighing more than a couple of tonne, but the M-class – especially in diesel guise – is certainly around the top of that particular pile and the latest refinements make it a better option than ever.