“What the heck is that?” is the reaction so far to the BMW 5-Series Gran Turismo.

But once people have a look inside, they’re not entirely averse to the big new BMW and its oddball styling. The 5-Series GT is a designer mashup of a big sedan, hatchback and crossover, all wrapped in a sloping fastback roof. While it wears a 5-Series badge, the car is actually much more closely related to the flagship 7-Series: It has the 7’s platform, its 400-horespower twin-turbo 4.4-liter V-8 engine and other lucky-7 goodies such as 4-wheel steering and a computerized suspension that lets the 5 GT handle flatter than a drill sergeant’s crewcut.

Inside, the 5 GT seats either five passengers or four -- the latter if you choose the deluxe rear seat with a fixed center console and a pair of plush, deep-reclining bucket seats. But the most eye-catching bit is the ingenious two-hatches-in-one arrangement: A rear hinged gate opens like a conventional trunk; hit another button, and a much larger hatch opens to access the full cargo area.

It all adds up to an enormous 5-door hatchback with a slightly elevated stance, a concept that Honda is also exploring with its new Accord Crosstour. Of course, the BMW costs more than double the Honda’s price, starting at an estimated $66,000. But come spring, BMW will offer a more affordable 535i GT model, likely starting in the mid-$50,000 range. It’ll be equipped with a new single-turbo 307-horsepower 3-liter inline six that will eventually step in for the current twin-turbo six in variety of BMW models. (And that new engine had better be good, because the current twin-turbo is one of the world’s great engines for both performance and relative fuel efficiency).

The question is whether buyers have any interest in a luxury fastback that recalls a modern take on the Lexus IS 300 SportCross or the Saab 9-3 Sport Combi. You’re forgiven if you don’t remember the Lexus or Saab; so few made it off the showroom floor to make any impression whatsoever. And BMW buyers already have a dizzying array of choices in sedans, wagons and crossover SUVs, from the 5-Series wagon to the X5 and X6 crossovers. Still, while some purists have already whined about BMW’s latest entry, BMW heard a lot of the same flak when it released the X5, its first SUV. We know how that one turned out; whatever you think of the merits of 2.5-ton crossovers, the X5 became a class benchmark for performance, and one of BMW’s best-selling vehicles.

The 5 GT is certainly far more of a niche model, unlikely to top more than 5,000 sales a year. But for buyers, since when did more choices become a bad thing? Clearly, new offerings like the X5 haven’t prevented BMW from steadily improving its terrific 3-, 5- and 7-Series cars, not to mention the high-performance M models or the new Z4 roadster. So until BMW announces that the M3 is going to become a family minivan instead, I'm prepared to cut it some slack.