Porsche has built many different cars over the years. Big ones, small ones, scarily fast ones and engagingly fun-to-drive ones, but I can’t remember one that left me as confused as this new Panamera.

It is the automotive equivalent of a duck-billed platypus. It’s wider and longer than a Porsche Cayenne but seats only four. Porsche cites the Mercedes-Benz S-class and BMW 7-series as key competitors but its body configuration is that of the humble hatchback. The S version I drove has essentially the same 4.8-litre V8 engine as the Cayenne GTS but when sales start this September, Porsche is going to ask an extra £17,673 for it.

Until I arrived at Porsche’s Stuttgart factory, I’d seen only photographs of the Panamera, but can now report it looks no better in the flesh. It’s been a long time since Porsche has made an attractive car, but the Panamera, which looks like a 911 that’s been magnified and then melted, is unquestionably the ugliest vehicle Porsche has made.

The inside looks marvellous, all low-slung and snug like a proper sports car, but as opulently trimmed and expertly finished as a limousine. Even here, though, there’s a flaw. Porsche says there’s no middle seat in the back because nobody would want to sit in it. Instead, it has provided the Panamera with four full-sized and supremely comfortable chairs.

If you sit in the back, you will marvel at how much headroom there is and the fact that there’s no shortage of legroom. The problem is that because you sit so low, the headrest for the front seat appears in the middle of your field of vision, and because the windscreen is so shallow you can’t see outside by peering over the top. Unless you elect to list sideways like the tower of Pisa, your view forward is severely restricted.

Dynamically, Porsche finds itself on surer ground. Until a base model V6 appears next year, this 400bhp Panamera S serves as the entry level. It will be joined by a four-wheel-drive 4S costing £77,269 plus a 500bhp turbo priced at £95,298. Porsche’s double-clutch PDK transmission is standard on the two more expensive Panameras and expected to be an option on all but a tiny proportion of S models. The engine and PDK box work effectively but unspectacularly (though Porsche infuriatingly insists on placing buttons on the steering wheel rather than paddles behind it).

The engine in the S offers performance commensurate with the price tag and a smooth note, while the PDK snaps efficiently between its ratios in both manual and auto modes. Commendably it’s also the first multi-cylinder motor with an auto gearbox to be fitted with stop-start technology.

The real magic has been saved for the chassis. With the Panamera, Porsche has set a new standard among big saloons for combining the usually diametrically opposed interests of ride quality and handling. This is a large and heavy car but it never feels it: on the contrary it feels agile. It has superb grip, the steering is brilliantly precise and the car maintains composure even on tortuous mountain roads. Then, when you hit the autobahn, you can almost see why Porsche claims its ride quality is comparable to that of a Mercedes S-class. It doesn’t quite match the Merc but it’s streets ahead of, say, an Audi A8.

Better still, the Panamera is admirably refined, cruising in hushed comfort at speeds that are illegal in Britain. The driving environment is good, too. The Panamera proves you don’t need iDrive-style central controls if you can offer a touchscreen and ancillary buttons, clearly labelled and located. And it doesn’t look a mess — it looks just right.

Which is why at first the Panamera is so confusing. It is a car of heroic abilities and calamitous failings and it takes a while for the fog to clear. When it does, it reveals a gulf between Porsche design and Porsche engineering. We saw this with the Cayenne, a space-inefficient and ugly brute that manages to drive better than any other SUV. If anything, these problems are even more pronounced in the Panamera.

Before you even consider writing the cheque, you’re going to have to reconcile yourself to its looks, and be happy buying a giant car that seats fewer people than a Ford Fiesta.

If you can square that, there is nothing else standing between you and a wonderful relationahip with the Panamera. In the way it manages both to ride and handle well there are lessons for every maker of large luxury or sporting cars.