What's new? For a car manufacturer capable of such effortless automotive sophistication, it’s reassuring to discover that BMW’s penchant for building brutal cars has been retained.I discovered this at the helm of the Z4M. At first I was surprised to find myself struggling to get along with it and was momentarily lost as to why this might be. The proposition, after all, was more than a little captivating, for this is more than a very powerful Z4 – it’s a Z4 to the power of M.Which means that finding a 338bhp, 3.2-litre straight-six motor under the bonnet is merely the most obvious of its many modifications. The suspension naturally benefits from stiffer springs and dampers, but it runs more negative camber, too, and a 10mm lower ride height. You’ll not be surprised to learn the tyres are fat: 225/45 R18 at the front and 255/40s at the back. Like other M cars it opts out of using the run-flat boots found on most other BMWs. Why? Run-flats are heavy and push unsprung mass through the roof, an absolute no-no when designing a high-performance car.Interestingly, the M-division has also concluded rightly that the standard electric power steering of the Z4 is not good enough for M purposes and replaced it with a conventional hydraulic system. The standard Z4 differential has also been replaced by the M3’s wondrous speed-sensing diff. The brakes, meanwhile, are those developed for the M3 CSL.What's it like? BMW is bullish about this car. Although aimed squarely at the Porsche Boxster S, it has priced the Z4M at £42,950, £4230 more than its rival. When asked about this strategy, BMW points to the fact that its car has a substantial 62bhp more than the Porsche, while presumably hoping no one notices that, at 1485kg, it is 140kg heavier than the Boxster. The difference in their power-to-weight ratios is a rather less conclusive 23bhp per tonne.Still, no one’s going to get sniffy about the way the Z4M goes, not when 62mph is only five tyre-shredding seconds away. No, my problem was at a more conceptual level. Try as I might, I just couldn’t get into the groove with it. I tried guiding it across the Spanish landscape as I would a Boxster S, but found myself missing apexes, turning in to corners too late, constantly having to correct my position on the road.Had a handy racetrack not presented itself, I might still believe the fault lay with the car rather than me. But on the circuit I discovered that trying to flow with the car and steering it smoothly was about as pointless as wearing sunglasses in bed. It would simply magnify all the problems found on the road, understeering stubbornly and leaving you wondering where on earth BMW went wrong.In fact, all it really needed was a different approach: a brutal approach. Instead of throttling back to stop the nose peeling away from a corner, you do the reverse and use judicious amounts of throttle to drive through the understeer, kicking the tail wide and into one of those drifting powerslides that look several times more heroic than they actually are. Treated like this, and once I’d convinced myself that the differential would allow insane slip angles without actually letting the car spin, it drove in much the same way you feel that TVRs should but all too rarely do.Informed and enthused by my discovery, I removed the Z4M from the track and applied what I had learned in diluted form to the medium of the public road. And do you know what? The Z4M transformed in my head from a borderline disaster to what it always promised to be: a seriously good-fun roadster.Should I buy one? Even though it and the Boxster S take diametrically opposed routes to the provision of driving pleasure, this does not mean one is necessarily right and the other inevitably wrong. Indeed, if you get your thrills from the delight of feeling the back of the car move and your reassurance from the knowledge that the car has enough basic agility and suspension sophistication to allow you to round it up with ease, then the Z4M driven with the right measure of controlled savagery provides a kind of pleasure the Boxster S driver will never know.And then there’s the enduring delights of that engine, which might be in its sunset years but still provides a searing soundtrack to accompany your progress, not to mention solid thrust over a 5000rpm powerband rising to an 8000rpm crescendo of which I will never tire.But I might get weary of its relentless animalistic nature. Fun though the Z4M can be on the right road or track, this is no substitute for the sensitivity, precision and feel imparted so freely by the Boxster S. However and wherever you drive it, you will never be as at one with the Z4M as you will in a Boxster S.That is not to say that the Z4M is any approximation to a bad car. The first obligation of any car wearing the M badge is to possess the capacity to thrill its driver and, flaws and all, that’s a commodity the Z4M possesses in spades.