There are sedans, luxury sedans, sporty sedans, and a fourth kind known only to people who get on their hands and knees inspecting exhaust pipes. Enter the sleeper sedan.

Sleeper sedans are the wolves in country club polos. Sometimes, they're cloaked in the same Subaru, Ford, and BMW sheet metal you rent from Zipcar or Hertz. And like how investment bankers party at strip clubs and charge their firms for "miscellaneous sundry," sleeper sedans are very discreet about providing entertainment, legal or otherwise.

Remember the first Taurus SHO from 1989? It appeared to be the average family Ford, but with a fast-revving Yamaha V-6 and five-speed manual, it was no commuter ride. The new Mercedes E63 AMG, with its four exhaust tips and lowered springs, looks a hair sportier than the cushy E-Class. Then you switch to the left lane, the transmission drops three gears, and in a few eye blinks the needle slams to 140. It's so smooth and easy, my mom could still be playing Angry Birds in the backseat and never notice.

The sleeper sedan we're driving today isn't a $100,000 Mercedes. In fact, there's no hood emblem or logos to call it anything. It sort of looks like a Mercedes, with its curved headlamps and horizontal lines on the grill. But from the side, it could be a taller BMW 5 Series from the last model year. And from the rear quarters, we're wafting scents of Infiniti M56. It's sleek, squat, and wears incredibly large tires for what appears to be a humble luxury car.

This is the Hyundai Genesis R-Spec, the sleepiest four-door of them all.

While its designers were inspired by the industry's best cars, they ended up with a style as flavorless as dissolved fiber powder. If you were renting a luxury car, the Generic — sorry, Genesis — would be the "Or Similar."

Then again, no one knows how much fun you're having in a Genesis, including the insurance companies. As everyone ignores my silver test car, I'm exiting the parking lot with some enormous twist. The traction control is fighting 429 horsepower, and after a little wiggle, the R-Spec points straight, fires off a few gears, and flat-out goes.

Most midsize luxury cars require at least 60 grand to pull that kind of stunt. But this rear-drive, V-8-powered Hyundai — let's repeat that again, a Korean-built Hyundai — is out the door fully loaded for $47,000. That includes the 8-speed automatic, slice-and-dice steering, gobs of grip, and potent brakes. Driving the Genesis feels like stealing groceries in the self-checkout lane. Have we bagged an AMG and rang up the V-6 instead?

Yes, in the buttery-smooth shifts, soft leather, hushed road noise, the V-8's near-silent idle, and long list of interior amenities. Sure, the bowed center stack is copied from the S-Class, but the infotainment controls, a blend of Audi and BMW, are remarkably easy to work. Xenon headlamps, power everything (including the folding mirrors and tilt/telescoping wheel), heads up display, radar cruise control, heated rear seats, HD radio, and keyless start are standard. There's no dancing around $3,000 "premium" packages on the R-Spec — it's all here.

Most of it, anyway. The cooled seat goes to the driver and not the front passenger, and not all of the materials — the rougher plastic lining the center console, the cheap-looking steering wheel, and ultra-bright LED dome lamps — are worthy. The seats are better than most Hyundais — which is to say, they're not completely flat and unsupportive — but you won't be snug around corners, nor will you tolerate sitting here for hours.

Despite its quick and generally agreeable behavior, the transmission has a notable omission: There's no sport mode or paddle shifters. I'm aware this is a sleeper sedan, but can't the gearbox stay awake for a few seconds? Instead of holding the engine within its peak torque range, near the 5,000-rpm mark, the R-Spec would rather upshift and waft along in sixth or seventh. Shifting through eight speeds with the gear selector is a slow chore you'll try once, and then give up. I'm not expecting Mercedes-style telepathy, where the car always picks the right gear before you even ask. We're talking about a basic software upgrade that'll make this sweet engine sing to high heaven.

The other downgrade, besides the kooky startup and shutdown chimes, is the tough ride from the hunkered suspension. This Hyundai is more like a Porsche Boxster than a refined luxury sedan, and not for the better. While rewarding on well-paved roads, the R-Spec shakes uncomfortably over mild to roughly-patched surfaces. Expect some kickback from the steering column over larger ruts, too. The base Jaguar XF, at a few thousand more, strikes a superior balance between ride comfort and handling agility. All of the European sedans win here.

For the time being, they'll keep winning. Luxury buyers will choose loaded 3 Series and A4s and see the larger, faster Genesis R-Spec as a trade down. It's an impressive horse with no name.

Hyundai's class-leading warranty and value-for-dollar can catch on — Lexus proves it — but they'll need several more generations of great cars to be noticed above the $40,000 fold. Put a confident face on the Genesis, and you'll see this sleeper truly come alive.