At first, it was difficult to take seriously what the Jetta BlueMotion Technology was trying to tell me. If the fuel economy readout on the instrument panel was to be believed, it was proving to be almost impossible to undertake any kind of journey without averaging more than 70mpg.Holy mackerel. The official combined figure for the car is 67.3mpg. I hardly ever match official combined figures, but here I was beating this one on a regular basis. At times I even nudged towards the extra urban figure of 78.5mpg. This was far more impressive than anything I'd previously recorded in any hybrid, or (as far as I can remember) any diesel, even ones much smaller than the mid-sized Jetta.The first two responses that occurred to me were, on the one hand, to sing a loud hosanna and, on the other, to declare, "Well, look at that. Volkswagen has obviously created the world's least accurate trip computer." The third response - rather more practical, I think you'll agree - was to take some measurements.And, what do you know, they came as close to matching the car's own readings as makes no difference. Assuming that the indicated and measured figures confirm each other, I'm persuaded that I really was getting more than 70 miles from each gallon of diesel.Except that one time. The time I went haring up and down a 30-mile country road, one with many a steep hill, one where a car of the 104bhp Jetta's modest performance had to be driven as hard as it would go in order to be able to overtake safely.That time it dipped down to 58mpg. Hah! I think I can count the number of cars I've driven this year that can average 58mpg driven gently on the fingers of one hand. For that reason as much as the incredible economy in more normal conditions, I wanted to hug the Jetta and squeeze it and call it George.Very little else made me want to do that. I quite like the Jetta, and I was sorry to see it go, but it is a very long way from being Volkswagen's best car. For one thing, it doesn't have anything like the quality feel you might expect of a Golf with a boot (which is essentially what it is, despite the fact that the two models do not share even a single body panel). In this respect it feels more like a Renault or perhaps a Vauxhall than a VW.The driving experience isn't great, either, and that's largely because - in a fashion that was once typically German but is less so these days - the front suspension is significantly underdamped. This makes the car lurch when, without any great effort and at no extra expense, it might have been made able to glide.Strangely, both the underdamping and the slightly vague steering become less of a problem as you start pushing harder. In fact, in really strenuous circumstances the Jetta actually becomes surprisingly sporty. However, since I don't think many owners will want to investigate this, I couldn't say it's much of a recommendation.The let's-not-make-it-look-any-more-like-a-Golf-than-we-have-to styling is quite effective, and to me the Jetta is particularly handsome in profile. The most obvious problem is that the rear window is quite shallow, so it's more difficult to see what's directly behind you than you might expect.A secondary problem is that there's no rear wiper, which is a pain in wet weather. But if I'm going to criticise the Jetta for that I also have to criticise all other saloon cars at the same time, since none of them have rear wipers either.I did get used to these flaws, in some cases rather grudgingly, and there are compensations: there's not much in the way of noise apart from a bit of a rumble on coarse road surfaces, the engine pulls very well from low revs, and the front seats are absolutely brilliant, with excellent side support.None of this alters the fact that, on the whole, the Jetta is rather a disappointing car. But it could be a much worse one and still be worth buying purely because of the staggering fuel economy. If it can beat 70mpg more often than not, it can also pour cold tea on to my trousers every five miles if it likes. I'd still have one. Engine 1598cc, 4 cylinders Power 104bhp Transmission 5-speed manual Fuel/CO2 67.3mpg/109g/km Acceleration 0-62mph: 11.7 seconds Top speed 118mph Price £19,530 Details correct at publication date