It's been widely noted that while there are 22 different hybrid cars currently on the American market (with the 2012 BMW ActiveHybrid 5 about to join them), nearly 50 percent of the category's sales are captured by one car, the Toyota Prius. Why do you think that is?

I think it's pretty simple. The Prius' pitch for your monthly payment is as elemental as possible: Want truly fabulous mileage (a combined 50 mpg) at a moderate price premium? Here I am. Think of it as better mileage on one hand, and its slight price premium on the other. And the tradeoff makes sense to a lot of people.

Cars such as the Lexus LS 600h L, the Porsche Panamera S Hybrid, and the BMW ActiveHybrid 5 I've just driven in Lisbon, Portugal, are slipperier characters to get your hands around.

I'm not saying the ActiveHybrid 5 (even the name is complicated) isn't an extraordinary technical feat, an authentic attempt to do good, and all in all, a wonderful car. It really is. But listening to its argument is like enduring these all-things-to-all-people politicians we're hearing at the moment. Want a fast sedan? "Grab your helmet." A green car? "I brake for polar bears." Luxury? "May I bring you your slippers?" Practicality? "I laugh as I pass gas stations."

That's quite a collection of hats to simultaneously wear.

Like the existing 7 Series hybrid, the ActiveHybrid 5 is an expensive proposition. At an estimated $61,845, it's about $8000 more than a similarly equipped 535i using the same basic, turbo-charged, direct-injection Valveltronic engine. But unlike its gas and electric stablemate, the ActiveHybrid 5 is a genuine full hybrid -- meaning it can electrically propel itself with the engine as a non-combusting passenger for about 2.5 miles and up to 37 mph, assuming you don't get frisky with the throttle. In this scenario, you're being motivated by the liquid-cooled 54-hp electric motor residing within the bell housing. It's energized by a 1.35-kW-hr (0.68 of it is available) lithium phosphate battery from Massachusetts' own A123 Systems, and it's cooled by the air conditioner's refrigerant. (Symbiotically, the battery's energy also supports the air conditioner.) The battery resides within the trunk, between the wheel wells, where it consumes 28 percent of the cargo space, though what's left is still a credible cargo hold. Daringly, BMW claims its 96-cell battery will last the life of the car -- probably why the battery is cycled through a cautious 50 percent of its state of charge. (I'm not sure if this says good things about the life of the car, however.)

Accelerate in a more BMW-like manner and the 302-hp six awakens and silkily couples (via a clutch) to the motor. Crudely clomp your foot down and the combination will twirl the needle to 60 mph in a claimed 5.9 seconds. A good number, but one that undersells the performance of this car, because the electric motor's instant response gives the combination a viciously sharp edge.

I've always felt that an engine's reflexes are just as important as its outright horsepower, not only for passing maneuvers, but also for adjusting the car's attitude when enthusiastically attacking corners. By being upstream of the eight-speed transmission, the motor isn't always hopelessly wound-out at higher speeds, but, depending upon the specific speed, repeatedly cycled through its rev range. While the Prius' artfully elastic interplay between engine and motor is great for urban driving, it won't do for a sedan that can hit 155 mph.

Once the accelerating is done, a second clutch between the electric motor and transmission allows the ActiveHybrid 5 to "sail" at up 50 mph (100 mph in fuel-saving/EV-oriented Eco Pro mode), and at red lights, its auto starting and stopping is utterly seamless. The brake pedal shows no sign whatsoever of regenerative braking's infamous mushiness.

And this is exactly what's impressed me most about the ActiveHybrid 5: its...software. The car's tally of technical hardware is unquestionably considerable. But the tougher challenge is being able to subtly glue them together with software. I can't remember how many times my co-driver on our test loop muttered, "I'd never know this car is a hybrid." So a bow here to the software code writers. And by the way, this very drivetrain will soon be plumbed into the 3 Series.

That said, the navigation system's software may be even more remarkable. Where it's available, topographical information is continuously assessed to maximize the hybrid's performance and efficiency envelope. For instance, while climbing a hill, the ActiveHybrid is smart enough to know it'll soon be regening downhill, so it more freely spends its trove of electricity. And if you've plotted a route, the system will top off the battery in anticipation of those last few miles where you'll silently glide through your neighborhood. The car thinks ahead better than most people.

The BMW ActiveHybrid 5 is visually distinguished by its matte chrome tailpipes; galvanized kidney grille slats; "ActiveHybrid 5" lettering on the C-pillars; an available Bluewater metallic paint color; and low-drag, 18-inch Streamline light-alloy wheels.

We're left with the sticky question of why BMW didn't just bolt a diesel to engine cradle instead. And here you either comprehend this BMW's multi-column spreadsheet of advantages and disadvantages, or you just quit and click delete. The ActiveHybrid's 12-13 percent better mileage compared with the 535i (about 28 mpg combined) is no match for what a turbo-diesel could do. But on the other hand, the hybrid's combined horsepower (335) is roughly 35 more than the 535i's, and it weighs more than 300 pounds more. And there's that instant throttle reaction I mentioned; the car's sometimes silent operation; and its topographical intelligence. This is not a simple, Prius-like calculation, and as cars and their drivetrains get ever more complicated, the confusion is only going to get worse. Fortunately, there's one thing about the ActiveHybrid 5 that isn't debatable: Its driving experience absolutely is worthy of the marque's performance heritage.