The fact that the Z4 is so radical is important. The car it half replaces, the disappointing Z3, drew a withering storm of hairdresser jibes. The radical looks of the Z4 are BMW's way of telling us that this is going to be different: this car will be every bit as good to drive as it is demanding to look at.

Underneath the Z4 lurk familiar 3-series suspension components. There are struts at the front plus BMW's clever multi-link 'Z' axle at the back. Settings are tweaked with the aim of giving a firmer dynamic character – further facilitated by a structure BMW claims is 259 per cent stiffer than the limp and wobblesome Z3. The quoted figure of 14,500 Nm per degree of distortion makes it better than most tin top saloons.

The Z4 is also aimed at a different market to the Z3. There won't be any four cylinder versions, the range will be entirely made up of 2.5- and 3.0-litre six pots, offering 192bhp and 231bhp respectively. Officially this is because three quarters of worldwide Z3 sales came with a six and, being a bigger and more expensive car, no reason was seen to fit the smaller engine to the Z4.

Unofficially the gap is because of a soon-to-be-announced smaller BMW roadster, likely to be badged Z2, that will offer entry level soft-top thrills.

Prices for the Z4 will be 'about 10 per cent' over the equivalent Z3s, suggesting the 3.0-litre version will cost about £30,500 when it comes to the UK next spring. Which is dangerous territory when you remember that the basic Porsche Boxster 2.7 is only £31,450. To have any chance, the Z4 will have to be exceptional.

The Z4's exterior styling is likely to split opinions and possibly even long-lasting friendships. But the cabin's design is unambiguously excellent. A long, lozenge shaped dashboard comes finished in either pretend metal or pretend wood finishes.

Roof operation is quick and painless, the simple folding fabric stowing itself in about eight seconds under one-touch powered operation. You don't even need to unclip it from the windscreen rail.

Roof up refinement is excellent, even at a brisk 90mph motorway cruise. Although without the bulky optional wind deflector the cabin gets a bit gusty with the canvas stored.

Our test car was the range-topping 3.0-litre which, as always, is a friendly, charismatic unit. Rumble becomes whoosh becomes a positive zing as you ascend the revs, while a nice, flat torque curve also makes relaxed cruising a painless process.

Brakes are firm and effective and the gearshift has a nice, solid action – both good sportscar cues. The 3.0-litre's six speeder also means some serious motorway gearing, and at 25kg lighter than its Z3 precedessor, also makes for surprisingly keen fuel economy and emissions figures.

Compared to the mouthy, trouser-free Z3, the Z4 is a vast improvement. But is it better than a Boxster? That would be a close call – although the Stuttgart coat of arms will always win out in the wine bar.

Strength: Performance and driveability
Weakness: Extreme styling
Opportunity: To win back sportscar enthusiasts driven away by the Z3
Threat:Z3 image hangover
The USP: Charismatic sportscar
Price: £24,000-£30,500 (est)
Engines: 2.5-litre, 192bhp 6-cyl; 3.0-litre, 231bhp 6-cyl
Transmissions:5-spd, 6-spd manual,6-spd paddle, 5spd auto opt; rear-wheel drive
Performance: 0-62mph 7sec, 5.9sec
Safety:Stability control, traction control, dynamic drive control, four airbags
Dimensions: Length: 4091mm
Width: 1781mm
Wheelbase: 2495mm
Rival:Boxster, SLK