A phenomenal engine such as the 2010 BMW M5's race-bred 500-horsepower V10 is typically enough to win enthusiasts over. Look at the muscle car era, for example -- its beloved icons are little more than enormous V8s strapped to the bare minimum in rubber, sheet metal and suspension bits. In the realm of super-sedans that cost close to $90,000, though, the stakes are considerably higher, and the M5 turns out to be not so super after all. Yes, that V10 is a thing of beauty, but the M5 is otherwise missing too much of the expected BMW DNA to earn our recommendation.

The problems start with the mandatory variable-assist and -ratio steering, which is a member of BMW's "active steering" family -- a dirty phrase in the eyes of 3 Series and 5 Series enthusiasts, who tend to avoid these newfangled systems like the proverbial plague. Driving the M5 is a reminder why. There's so little of BMW's trademark steering feel here that it could be mistaken for electric power steering, and the variable ratios sometimes feel out of step with driving conditions. This is a passable setup by the standards of mere automotive mortals, but when we see M badges on a car's trunk lid, we expect more.

Then there are the two transmission choices, neither of which is particularly palatable. The standard seven-speed sequential manual gearbox (SMG) is a single-clutch automated manual -- a dwindling breed in this era of slick multiclutch gearboxes. In fact, BMW now has a dual-clutch unit of its own in the M3, but the M5 soldiers on with the old-school SMG. On the bright side, SMG will rip off spine-tingling rev-matched downshifts all day long. Upshifts, however, are never smooth, and they usually involve unseemly lurching -- particularly at low city speeds. A six-speed manual transmission can also be specified, but it overheated in a test car we had a few years ago, and it also comes with a non-defeatable stability control system, which is befuddling in light of the M5's super-sedan identity.

Lest you conclude that we've been pounding steins full of M5 haterade, hear this: In most other respects, the 2010 BMW M5 is a stupendous car. As noted, the 5.0-liter V10 pumps out an otherworldly 500 hp, and it sounds as good as it goes, particularly as the stratospheric 8,250-rpm redline approaches. There are no fewer than 279 different vehicle settings according to BMW, which means you can fiddle with the M5's power, throttle, transmission and suspension settings to your heart's delight. The incredibly supportive and comfortable seats are quite possibly the best all-around automotive chairs in the world. Even the newly hard-drive-based iDrive is something to brag about now, thanks to an updated interface and menu structure that are actually intuitive and useful for a change.

Without a doubt, the M5 is one of the planet's most capable super-sedans. And upon its debut, we thought pretty highly of this latest M5 icon. But with more time under our collective belt, we've become more attuned to its decidedly un-BMW-like shortcomings. And overall, we think there are simply better choices. Sizing up the field in this loosely defined segment, we'd rather have Mercedes-Benz's C63 AMG or E63 AMG, Jaguar XFR, BMW's own M3 sedan or even the Cadillac CTS-V. Porsche's new Panamera is another impressive contender. Here's hoping that the soon-to-be-redesigned 5 Series yields a properly lust-worthy next-generation M5.

The 2010 BMW M5 is a high-performance variant of the midsize 5 Series luxury sedan. Standard equipment includes 19-inch wheels, performance tires, adaptive xenon headlamps, front and rear parking sensors, M-Sport settings, auto-dimming mirrors, a sunroof, dual-zone automatic climate control, a power tilt-and-telescoping steering column, heated front seats, power sport seats, front-seat memory, leather upholstery, the iDrive electronics interface, a navigation system with real-time traffic and voice commands, Bluetooth and a 13-speaker surround-sound system with a CD player.

Options include soft-close automatic doors, keyless ignition/entry, fold-down rear seats, upgraded power front seats, a power rear sunshade and manual rear side shades, extended leather trim, ventilated front seats, heated rear seats, a heated steering wheel, a head-up display, an upgraded sound system, satellite radio and an iPod interface.

The rear-wheel-drive 2010 BMW M5 is powered by a scintillating 5.0-liter V10 that pumps out a maximum 500 hp at 7,750 rpm and 383 pound-feet of torque at 6,100 rpm. Interestingly, the full 500 hp is only available when selected by the driver using the MDrive performance settings; the default setting is 400 hp, the same output as the previous M5's V8. The standard transmission is the seven-speed sequential manual gearbox (SMG), a single-clutch automated manual that can be placed in a fully automatic mode or operated manually via the gearshift lever or steering-wheel-mounted paddles. A conventional six-speed manual transmission is a no-cost option.

In performance testing, we've clocked the SMG-equipped M5 from zero to 60 mph in 4.8 seconds, while a manual-equipped car accomplished the same feat in 4.7 seconds. Estimated fuel economy, should one care, is an expectedly poor 11 mpg city/17 mpg highway and 13 mpg combined with either transmission.

Standard safety equipment on the 2010 BMW M5 includes stability control, full-length side curtain airbags and front-seat side airbags. Rear-seat side airbags are optional. The government slapped the structurally similar BMW 5 Series with a disappointing three out of five stars for driver protection in frontal crash tests, but a perfect five stars were awarded for front passenger and side-impact crash protection. The Insurance Institute for Highway Safety gave the 5 Series its top "Good" rating in frontal-offset crash testing, but side-impact testing was a mixed bag: The 5 Series without the optional side airbags scored a second-worst (of four) "Marginal" rating, while adding that option brought the score up to "Good."

The 2010 BMW M5's 5.0-liter V10 is a high-revving wonder of modern engine technology, yowling its way to that 8,250-rpm redline with an exquisite combination of ferocity and refinement. However, neither transmission choice is appealing. The six-speed manual is certainly more rewarding than the lurch-prone single-clutch SMG, but stability control is disappointingly undefeatable on manual-shift M5s. As noted, the steering is oddly lacking in feel and consistency for a BMW rack. If your heart's set on a BMW super-sedan, we'd recommend taking a close look at the M5's little brother, the more-enjoyable-to-drive M3 sedan.

The M5's interior is tightly constructed with high-quality materials, and there's enough room in the backseat for a couple adults to ride all day in comfort -- not bad for a car with this much performance potential. The newly revised hard-drive-based iDrive system is finally an infotainment interface to be proud of thanks to additional physical buttons around the control knob and a new menu structure that just makes a lot more sense.

The standard 16-way-adjustable front seats are excellent in their own right, while the optional M multifunction seats are some of the best chairs presently for sale in terms of support, comfort and adjustability. However, the M multifunction seats' active side bolsters, which move inward to brace front passengers against cornering loads, can be distracting at critical moments. We'd advise you to turn this feature off and leave the adjustable bolsters at your preferred setting. The trunk's luggage capacity -- likely not the M5 shopper's top priority -- is a decent 14 cubic feet.