Every now and then, an automaker will roll out a new vehicle that shapes up as a mystery to me.

For 2007, the all-new GMC Acadia is the object of my misunderstanding.

I look at the '07 Acadia and see it covered in question marks, like the outlandish suits the Riddler villain used to wear in the "Batman" TV series in the 1960s.

Maybe I'm just dense. After all, I never understood pet rocks, Rubik's Cube or, more recently, "American Idol" ... and yet they have appealed to millions.

And it's not that the Acadia is not a quality machine. Actually, after a week behind the wheel of one, I thought it was exceptional on several fronts.

A roomy interior -- it can hold up to eight passengers, although seven is standard on the tested Acadia SLT-2 with all-wheel drive -- is stuffed with comfort/convenience amenities.

Standard goodies that came with the tester's $37,370 starting price included leather seating surfaces, Bose speakers, a power liftgate, heated windshield wiper fluid, triple-zone climate control, heated/power exterior mirrors and a tire pressure-monitoring system, to name just a few.

On the roll, the Acadia's 3.6-liter V-6 with 275 horsepower performed well. No, the power plant is not a road scorcher and fuel economy was a not-so-great 17 miles per gallon in the city and 24 mpg on the highway.

But the V-6 held its own in most driving conditions, and the 22-gallon gas tank will take regular unleaded.

Body sway on this vehicle, which is longer than 200 inches and tips the scales at nearly 5,000 pounds, was negligible. Road noise had a tough time penetrating the interior cabin. Road imperfections had similar difficulty getting to the seat bottoms inside the Acadia.

The Acadia's six-speed automatic transmission performed seamlessly and flawlessly.

Exterior styling is pleasant, including the bold front grille one expects from a big light-truck producer like GMC.

Interior controls are nicely laid out and easily understood. In the third-row seat, where many seven- and eight-seat vehicles give passengers the sardine can experience, the Acadia has a wealth of space for even large adults to stretch out. Also, second- and third-row seats slide to adjust space accordingly.

So, what's the mystery?

Well, there's the fact that General Motors calls the Acadia "GMC's first crossover sport-utility vehicle." OK, technically, there is some vehicle segment-crossing DNA in the Acadia, but it just felt like a big SUV to me.

I've read accounts by other auto reviewers who said the Acadia in no way looked like an SUV. Really? Looks like one to me, a big one.

Also, at a time when GM has been trumpeting the need to produce more fuel-efficient vehicles and fewer full-size light trucks, the timing on the new Acadia seems at best, peculiar.

And then there was this bottom-line sticker price on the tested Acadia -- $45,360. I stared at that big number for a full minute when I took delivery of the vehicle.

The tested Acadia's nearly $8,000 in options included things I could do without, and I started mentally checking them off in my mind: touch-screen navigation system (pricey at $2,145, but a plus), dual sunroof (uh, no thanks for $1,300), 19-inch "ultra-bright" aluminum wheels (absolutely no way for $1,295), DVD-based entertainment system (OK, give the passengers a break from my conversation for $1,295), high-intensity headlamps (good safety feature for $500), a trailering package (worth it for $425), "premium" paint (what's premium about an extra $395?) and a head-up display for the driver (I can save $350 and look at the gauges like most drivers do every day).

All things considered on the tester, I was wondering: Who would pay nearly $45,500 for this vehicle?

And it quickly came to me: Somebody who wanted an upscale, full-size SUV but didn't want to pay the $50,000-plus fare for luxury level SUVs made by Lexus, Mercedes-Benz and some others.

Mystery solved? Well, maybe.

I understand the idea of wanting a roomy, well-equipped SUV with good handling characteristics, made by a GM division with a reputation for building sturdy light trucks.

But if I were heading to the dealership to size up the Acadia, I'd keep track of those pricey options. Prospective buyers should decide what they want and what they don't.

That might take the mystery out of getting the Acadia you desire.

2007 GMC Acadia at a glance

Make/model: 2007 GMC Acadia AWD SLT-2 Vehicle type: Up to eight-passenger, four-door, all-wheel-drive sport-utility vehicle Base price: $37,370 (as tested, $45,360) Engine: 3.6-liter V-6 with 275 horsepower at 6,600 revolutions per minute and 251 foot-pounds of torque at 3,200 rpm EPA fuel economy: 17 miles per gallon city; 24 mpg highway (regular unleaded) Transmission: Six-speed automatic with overdrive Steering: Hydraulic rack and pinion Brakes: Power-assisted four-wheel, ventilated discs with anti-lock and other braking-enhancement features Suspension: Independent coil-over-strut type on front; independent linked H-arm on rear Fuel tank: 22 gallons Passenger volume: 152 cubic feet (estimated) Maximum cargo volume: 119.9 cubic feet Curb weight: 4,925 pounds Height: 72.8 inches (with roof rails) Length: 201.1 inches Wheelbase: 118.9 inches Width: 78.9 inches Track: 67.3 inches on front and rear Ground clearance: 7.4 inches Towing capacity: 4,500 pounds Tires: P255/60R19 radials Final assembly point: Lansing, Mich.