It's become an economic weather vane for the middle classes: the caricature transport for the thirtysomething family motorist moving up from the VW Golf or Audi A3.
In Britain, it has reportedly outsold the Ford Mondeo on several occasions. That's good news for Tony Blair as he prepares for an election.
Yet it also signals just how important the 3-Series is to BMW. In its plans to topple Mercedes from the premium market, the Bavarians have introduced several new models, with more to come.
The plan is to bring the model range up to 12, with the addition of coupe/SUV crossover and a sporty people carrier in the coming months. So far the new introductions have received mixed reviews. The 1-Series is considered sporty but a little too cramped in the back, while the X3 seems a rather pointless exercise.
Yet for all the extra customers these new models can bring in, future success still depends on bread and butter models like the 3-Series, which represents 40 per cent of all BMW sales.
The success of the small BMW has been noted by more than just the motoring populous. When rival Lexus launched its IS range, many suggested it was closely modelled on the 3-Series. Indeed the new IS introduced at the Geneva motor show earlier this month still bears several visible similarities to the BMW, suggesting the savvy Japanese know whom they have to chase.
Admittedly the 3-Series has put on a few kilos since the first generation appeared 30 years ago. Again this fifth generation model gets bigger again. An increase in the length of the car is largely to the benefit of the rear knee room while the use of run-flat tyres means a saving of 45 litres in the boot.
Sadly, not all of this goes towards the bootspace. New US rules about rear impact protection means that there's only 20 extra litres for luggage.
But does this extra bulk mean that it loses some of its driver appeal? Will the new 3-Series retain its class-leading crown? The answer has to be a firm yes.
The Bavarian remains a better built car than most of its rivals. It's also better finished than its predecessor, right down to the engine compartment where extra coverings have been used to protect wiring and the like.
On the road, the chassis has been stiffened by a further 25 per cent making it one of the most confident cars in its class in corners, with a good weight balance between front and rear. .
The fall back to four cylinders in the 320i means that it's slower than its predecessor, and lacks the comforting resonance of BMW's famous six-cylinders.
Power output is down from 168bhp to 150bhp. Some are suggesting that this fall in output may woo buyers over to the diesel versions. The final decision will be settled by which is more important to the buyer - power or cash.
A quick calculation based on the price difference of €4,400 between SE models and current fuel prices suggest that it would take the diesel owner about 300,000 km to balance out the higher price. So if it's just about the cash, then petrol is still the better buy.
However, the diesel has a lot more pace over its petrol equivalent, offering 163bhp, a 0-100km time of just 8.3 seconds and a lot more low down torque - 340Nm against 200Nm.
It's a pity to lose the six-cylinder and true petrolheads will move to the 325i or 330i. For the rest, the 320d should be considered. All feature a six-speed manual gearbox as standard and it's sporty, even if the 320i lacks punch in fifth and sixth gear.
If we had one major disappointment with the new car, it's the ride quality. BMW is at the forefront in pushing new technology - for example with its iDrive system, derivatives of which are now to be seen in competitor models. More recently it has become the flag bearer for run-flat tyres.
Since their inception, there has been a vast improvement, but on Irish roads we were disappointed with the harshness of the ride. This was all the more surprising given the relatively good ride from the Pirelli Eufori run-flats on the test cars at the initial launch in Spain.
As for the iDrive, BMW has decided only to offer it when satellite navigation is chosen. That will set buyers back between €2,590 or €3,360.
While it may be a worthwhile addition to the resale value of the car in years to come, given the relatively poor coverage of satellite navigation in Ireland at present -with many non-national roads and routes outside Dublin still not featured - there may be better ways to spend your money, such as 17-inch alloys to set off the car's sporty lines.
Interior trim has been improved to take on the sleeker lines of the 5-Series, and the cockpit and dials are stylish and easily legible. The gap between others in terms of interior finish has closed however, particularly with the likes of the C-Class. Limitations also remain with rear seat space.
Even with the extra length and legroom, it's really designed for two adults rather than three and further limited by the deep scallops in the sports seats.
Perhaps BMW's biggest challenge is to maintain its prestige and aspirational status while at the same time becoming more and more ubiquitous on our roads. Somehow the 3-Series has met this challenge head-on.
The stiffer chassis on the 3-Series makes it still the best driver's car in its class. Competitors will no doubt push to keep the pressure on. But the BMW seems up to the challenge.