BMW used to be the soul of simplicity. Two decades ago its cars basically came in three sizes: small (the entry-level 3 Series), medium (luxury 5 Series) and large (executive-class 7 Series). Styling seemed an afterthought. And in-cabin technology didn t require hours of slogging through an owners manual. What the carmaker did offer was a single-minded emphasis on performance driving.

But these days simplicity doesn t sell at least on the high end, as luxury marques load up on fancy features, from drowsy-driving sensors (Mercedes) to a Forest Air purifying system (Infiniti). So BMW has adapted. It has added more models. Bimmers now sport far more stylized lines, even (gasp!) curves. And high-tech enhancements have become a defining element most notably the NASA-worthy iDrive system, which controls audio, navigation and other functions. What hasn t changed especially with the rede-signed 535i, the midsize model we recently test-drove is its signature behind-the-wheel muscularity. The 5 Series s interior may seem to have been designed for the Grey Poupon set, with the requisite plush leather and the shiny wood or metal trim, but performance purists can still bank on BMW s high-revving, red-meat kind of drive (cue the growl of its six-cylinder, 300-horsepower engine) especially when they push the magic button. More on that below.

Until recently BMW hasn t had a lot of incentive to radically overhaul the 5 Series. After all, the company says, it s the brand s second-best-selling model and rakes in about half its total profit. But the 5 competes in a crowded class of well-regarded premium sedans, including the Mercedes-Benz E-Class, Jaguar XF, Audi A6 and Cadillac CTS. And sales of the model have dropped 38 percent year-to-date compared with 2009, as consumers continue to shy away from big-ticket outlays and some buyers have waited for the redesigned model. So for this 535i incarnation, BMW gave the styling an aggressive up-date, subbed in a more fuel-efficient engine and made a rare concession to the economy, bumping the price down $1,650, to $50,475.

Not that the Bavarians are giving away much, since most of the 535i s luxury and performance goodies are tucked into pricey option packages. In addition to purchasing a $1,900 navigation system and the usual sport ($2,200) and premium ($1,800) bundles, buyers can also pony up for a convenience package ($1,700), a dynamic handling package ($2,700) and a driver assistance package ($1,750) that includes such things as a blind spot detection system and a self-parking feature for those tight spaces. Of course, all these add-ons can add up. With BMW, the base car really exists for marketing reasons, says Ed Kim, director of industry analysis for AutoPacific. The option packages are where a lot of the profit is baked in.

Traditionally, a BMW driver is not someone whose idea of automotive heaven is coasting on a cloud. He prefers to feel the road and screech through the turns. With the 535i, BMW plays to the faithful, offering a six-speed manual transmission or an eight-speed automatic that can be used for clutchless manual shifting. (We tested the automatic.) And not surprisingly, the most rewarding feature is that optional dynamic-handling package that lets you electronically alter the performance of the car s suspension, transmission and engine. The push-button setting offers four modes, ranging from comfort, which your mother-in-law will love, to sport plus, which may make her want to jump out of the car. (Don t get any ideas.)

During our test-drive, it took all our automotive willpower to keep the 535i in comfort or normal mode for a few days, but we wanted to really feel the differences. In those initial days the 535i proved to be a plain-vanilla luxo-cruiser a placid, automotive Dr. Jekyll. But after we finally gave in and hit that wondrous console button, the words sport-oriented drivetrain and chassis settings popped up on the dashboard display, and a veritable Mr. Hyde emerged: The steering tightened. The acceleration quickened. (So did our pulse.) And the car s suspension system leaned into curves aggressively instead of wallowing through them. The 535i had been transformed into a totally different car one that absolutely demands driver involvement.

There s a price for this which shouldn t surprise experienced luxury-car buyers. To get the dynamic-handling package, you must first buy the sport package. Also, the 535i gets a fuel-economy ratings of 20 mpg in the city and 29 mpg on the highway, but that s in normal mode; sport-plus mode will likely offset those gains. (BMW won t say by how much.) Then again, that s probably a trade-off many Bimmer drivers are happy to make.