The focal point of any Jaguar is its cabin, and climbing aboard the S-type reveals what is, frankly, a mild disappointment. There's wood, for sure, but not as much as you might hope for, and it fights for position with much plastic whose quality varies from door trim to dash top to console. The wood has rather a 'stuck-on' feel to it, too; it moves when you press it, rather like the timber-effect trim moves in a top-spec Mondeo.
Neither do the dash and door casings have the tasteful hints of chrome trim that make the XJ's cabin so special. But the cabin is cosseting, and with small windows and the high scuttle there's a nostalgic sense of retro about the interior; it's not that spacious, nor is it particularly well-packaged, but for some reason these things don't seem to matter in the S-type. It's all about self-indulgence and a feeling of personal well-being: what it lacks in tacitly it makes up in close-coupled comfort.
The AJ6 3.0-litre V6 - Ford-based but heavily modified by Jaguar - is one of the most powerful of its type, with 240bhp developed at 6,800rpm, enough for a top speed of 146mph and 0-60mph in just 6.8secs for the manual. That top speed matches the BMW 528i's 147mph, but the acceleration time is considerably quicker than its 7.5secs.
Strangely, the V6's eager nature makes the 281bhp V8 in the 4.0-litre feel less muscular than its output suggests, and it performs with a searing V6 yowl that's muted but, you surmise, carefully tuned to please the discerning sporting driver's ear. Ultimately, it's not as smooth nor as wonderfully tractable as Alfa's 3.0-litre V6 in the 166, nor is it as good-sounding, but there's no doubting its potency.
With the V6, there's a choice of either five-speed manual or five-speed automatic transmission (at extra cost), while the V8 is auto-only. In manual form, the shift is light and slick with excellent ratios and it matches the V6 perfectly to create the bones of a finely judged sports saloon. Less impressive is the automatic which suffers a sleepy change and infuriatingly slow kickdown.
A snappier change could be achieved at the expense of shift smoothness: it's striking the right balance in the gearbox's governing computer that's the tricky bit -something the Technical Department is working on. You might expect Jaguar's engineers to conjure up something special in the chassis department, and, true to form, they have. Great steering, a wonderful ride (both at low speed and on the move) and supreme body control make for a relaxed and entertaining high-speed handler.
Our car had the optional CATS (Computer Active Technology Suspension) at a worthwhile £1,970 extra, including 17in sports alloy wheels and tyres. Rather than firm everything up to the intolerable, as is the case with so many so-called 'Sport' packages, CATS broadens the suspension's envelope of ability through careful tuning of springs and dampers.
So the ride is firm but not uncomfortable round town, wonderfully composed at speed on a twisty road and yet still comfortable on the motorway. I suspect, too, that nearer the S-type's limits, CATS will retain the car's inherent composure for longer, making for a safer drive.
So it's clear S-type buyers won't be disappointed, but the final crunch question remains: is it better than a 528i? Well, yes and no. A car that improves on the BMW would have to be pretty special indeed - and the good news is that the S-type matches it in many respects, testament to the fact that Jaguar scrutinised the Five closer than any other car in its benchmarking process.
Crucially, the S is faster and more characterful with a higher desirability factor and, for the moment, far greater exclusivity. But where the S isn't quite so good - the brakes, for example, which aren't as reassuring as we'd like, and in wind and road noise suppression, plus, of course, the all-important build quality - the Five powers ahead.
Quite simply, it's difficult to find any weak points in the BMW's arsenal, which means that, still, it is the most rounded, most accomplished car in the class. And despite the strongest challenge yet to its crown, the 5-series still sits pretty four years into its life.