It started badly. My first contact with the E 320 CDI estate was accompanied by a loud arthritic creaking as the door mirrors unfolded with the remote locking opening sequence. Acutely aware of Mercedes' struggle against charges of falling quality standards I feared the worst.The car I was preparing to drive cost more than £44,000 - hardly the price of a chuck-it-in-the back holdall - and even at its pre-options price of £38,045 any hint of inferior quality is unacceptable. When you buy a Mercedes you have a right to accept the best. Quality on a car bearing the three-pointed star should be as natural a feature as see-through glass - no exceptions.I went round the E 320 CDI load carrier with a fine toothcomb looking for flaws. I forgave the broken boot floor-lifting handle, snapped by some ham-fisted tester, and a loose rear trim panel could be put down to carelessness and not a quality shortcoming. But ill-fitting central console lids and the creaks and groans from the door mirrors were hard to accept. An irritating steering column squeak didn't help.The electrically folding mirrors infuriated me every time I locked and unlocked the car. The steering column squeak was loud enough to make itself heard through a corner at 60mph. This is a Mercedes estate car - creaks and groans should be confined to the Georgian antiques you carry in the back.No manufacturer is immune from quality weakness - Audi, BMW and even Lexus have had their low points. What is different about Mercedes is that it once held the quality high ground and the sad fact is that the company is no longer master of the art. Mercedes needs to recognise that and take action to stop sales haemorrhaging.I have every confidence this will happen. Why? Because I've just driven the stunning new B-Class MAV and experienced the solidity of the new CLS, SLK and CLK. Quality oozes from all four. What's more, the E 320 CDI is not the disappointment you might have thought. The big estate is a joy to drive, strong, powerful, quick, stable and comfortable. Capacity is enormous - 650 litres with the rear seats in place and a massive 1910 litres with them folded flat into the floor. That's impressive cargo space, though surprisingly nearly 300 litres less than the new B-Class.The heart of the car is all-new - a smooth three-litre V6 turbo diesel. The lusty old in-line six-cylinder common-rail turbo diesel was a real powerhouse. Noisy at cold start and gruff under power, it did its job without complaint with little more than a muffled grumble up front. But heavy throttle use made it sound unrefined.That's all in the past. The new V6 CDI is a real smoothy by comparison. It's 63lb/ft down in torque and, despite still being known as the E 320 CDI instead of the E 300 CDI it really is, gives away 200cc in capacity. But it doesn’t show because there's 20bhp more to play with from the smaller engine. Mated to the latest superb seven-speed Tipfunction automatic transmission, it turned in a blisteringly impressive performance.High-speed cruising is effortless, irrespective of load. Overtaking response is instant and accompanied by a satisfying and immediate downchange. As the power kicks in all you hear from the front is a soft growl. Not once in nearly 600 miles of motoring did I ever lack for power. It flowed right up to its 4750rpm limit.The 320 CDI is a big, heavy car. But the new 204bhp V6 CDI makes light work of its near 1.9-tonne kerb weight. Its 306lb/ft of torque is in full flow from below 2000rpm and stays as the revs rise. That means effortless hill climbing and overtaking. And the multi-link rear set-up with anti-squat and anti-dive geometry copes well. Air suspension and self-levelling kept the rear end in check when I loaded the car and the 320 CDI could be hustled along twisty B-roads with ease. Roll is minimal, adhesion high and ride, while on the firm side, absorbed the worst surfaces without complaint. Good credentials for a rear-drive cargo ship.Where you need restraint is in choosing your options. The superb COMAND APS cockpit management and navigation system is one of the best available, but expensive as a £1950 option. So too is the £1250 leather pack, the £620 Easy-Pack load compartment sliding floor system, £590 Parktronic installation and the £650 memory electric driver's seat and steering column adjustment package.But good things never do come cheap; despite its currently tarnished reputation Mercedes-Benz is far from being written off and the E320 CDI Elegance estate is a very good car. Engine 2987cc, 6 cylinders Power 224bhp Transmission 7-speed automatic Fuel/CO2 34.9mpg / 202g/km Acceleration 0-62mph: 7.3 seconds Top speed 155mph Price £38,045 Details correct at publication date