There's no doubt the Panamera is a very good car. What Porsche has achieved is impressive. It’s striking to look at and extremely fast, yet it can also carry four passengers and their luggage in luxury. Plus, it sits more easily with the German company’s brand values than the controversial Cayenne SUV does. However, the Panamera feels ever so slightly compromised. It isn’t as much fun as a 911, quite as comfortable as a Mercedes S-Class or nearly as capable as an Audi RS6 Avant. Most importantly of all, it doesn’t tug on your heartstrings quite like a Maserati Quattroporte.

The arrival of a new Porsche is always a special occasion – but the launch of the Panamera, the firm’s first four-door saloon, is a landmark event.

Following in the footsteps of the Cayenne SUV, it’s the latest example of Porsche expanding its range beyond core models, such as the 911 and Boxster.

At five metres long, the Panamera is a big car, and the famous German maker has some equally large claims about it, too, saying it’s a cross between a sports coupé, a limousine and an estate. That’s a tall order – more importantly, though, does it live up to the heritage of the badge?

Well, it doesn’t lack performance. Under that sloping nose lies a 4.8 litre V8, which is naturally aspirated in the S and 4S models, delivering 400bhp. But in the Turbo we tested, forced induction increases power to 500bhp.

Acceleration is incredible. Despite weighing two tonnes, the Turbo rockets from 0-62mph in 4.2 seconds. And there’s no let-up in thrust, even when the speedo is in triple figures.

On an unrestricted section of German Autobahn, we managed 175mph with little fuss. And at these speeds, the car feels amazingly stable. This is due to the downforce provided by the special ‘3D’ pop-up tail spoiler and a very sophisticated chassis.

The Panamera Turbo comes with air-suspension and Porsche’s Active Suspension Management (PASM). This allows you to opt between three settings – Comfort, Sport or Sport Plus. In the first two modes, the car can float a little.

But in the firmest setting, the Panamera is surprisingly agile. It corners flatly, there’s plenty of grip and the steering is responsive and direct.

Make no mistake, the four-door Porsche is hugely capable. Yet, it’s nowhere near as much fun as one of the manufacturer’s normal sports coupés.

So how does it measure up as a limousine? First impressions are good. Inside, you can’t help but be impressed by the quality.

The interior is so delightful it wouldn’t look out of place in a Terence Conran exhibition. And, of course, everything is equally well put together.

It’s really comfortable and roomy, too – even in the back. You could drive or be driven across a continent in the Panamera. However, you would be even more comfortable in a Mercedes S-Class or BMW 7-Series.

There are plenty of gadgets, though. Pleasingly, you don’t have to run the gauntlet of confusing menu-based systems, like BMW iDrive, to access them.

If you want to activate the climate control, you simply press a button. If you need to turn off the traction control, you press a button. And to alter the suspension, you press a button. Easy. The downside is the Panamera’s cabin is swamped by buttons. We counted more than 100!

Can this super-saloon really be as practical as a normal estate? The boot has 445 litres of space and, with the seats folded down, this increases to 1,250 litres, which is pretty impressive.

Annoyingly, though, you can’t actually fold down the central armrest between the two chairs. And this sums up the Panamera.

It’s nearly an estate, it’s virtually a limo and it’s almost a sports car. But therein lies the problem.

While it’s certainly an impressive piece of technology and a jack-of-all trades, it is, actually, a master of none.

Rival: Maserati Quattroporte
A true dual-mode sports saloon, the Quattroporte is equally at home on a twisty road as it is on a high-speed motorway. And thanks to its stunning body, it’s about as desirable as luxury cars get.