Six years after the Nissan GT-R officially came stateside, it's fair to say that this ultra-high-performance car is still completely bonkers. There's a 545-horsepower, twin-turbocharged V6 engine. A dual-clutch automated manual gearbox. An advanced all-wheel-drive system. An adaptive suspension. Nitrogen-filled tires. There's even an in-car performance meter display that was co-developed by the people who created the Gran Turismo video game franchise. What else could you possibly want?

Well, how about even more bonkers? For the 2015 Nissan GT-R, there's a new GT-R Nismo model. Meant to be the ultimate factory-produced, racetrack-going GT-R, the Nismo benefits from a variety of performance-enhancing upgrades. Nissan upped the V6's power output to achieve a truly over-the-top 600 hp, while the suspension has been retuned to be even more race-oriented. Nissan even went to the trouble to stiffen the Nismo's body structure and add special aerodynamic, downforce-producing enhancements, the most noticeable being a new rear wing that looks as if it could have come directly from Boeing.

Thankfully, Nissan also knows that not everybody wants just "more." And for them, the regular-strength versions of the GT-R are more livable this year. Improvements to the GT-R's suspension, as well as steering and brake hardware, have made the car more comfortable to drive every day. On the outside, both the front and rear ends have been given a face-lift that includes details like new LED adaptive headlights and a standard rearview camera. Inside, there's more sound-deadening material and a new active noise-canceling system.

This combination of the even more extreme Nismo model along with the slightly more refined standard version keeps the Edmunds.com "A" rated 2015 Nissan GT-R right in the mix of the best supercars available. It's still fair to say that it won't generate quite the same passionate experience that you get from the 2015 Porsche 911 GT3. Nor is it quite the value it once was considering the power and price of new 2015 Chevrolet Corvette Z06. The highly anticipated 2016 Acura NSX is another enticing alternative. But the GT-R is still very much bonkers, and for that, we're grateful.

The 2015 Nissan GT-R is a high-performance 2+2 sport coupe with seating for four passengers. It is offered in four trim levels, including Premium, a Black Edition and a Track Edition. A new, more powerful GT-R Nismo version makes its debut this year.

The entry-level Premium model's list of standard equipment includes 20-inch alloy wheels, summer-rated tires, an adaptive suspension, Brembo brakes, automatic LED adaptive headlights, LED running lights, a rearview camera and keyless ignition/entry. Inside you'll find dual-zone automatic climate control, leather/simulated-suede upholstery, an eight-way power driver seat and four-way power front passenger seat, heated front seats, cruise control, a 7-inch touchscreen display, Bluetooth phone and audio connectivity, a navigation system and an 11-speaker Bose sound system with a CD player, satellite radio and a USB/iPod interface. An active noise-cancelling system is also standard for 2015.

There are two optional packages. The Premium Interior package adds upgraded leather upholstery while the Cold Weather package gets you all-season run-flat tires and a special coolant mixture for faster engine warm-up.

The 2015 GT-R Black Edition features lightweight black alloy wheels, a carbon-fiber rear spoiler, Recaro front sport seats and unique black and red interior trim. The Track Edition is equipped much like the Black Edition, but includes competition-ready upgrades including firmer suspension tuning, a front spoiler, front and rear brake cooling ducts, a carbon-fiber trunk lid and specially bolstered front sport seats. The GT-R Premium's option packages aren't available for the Black or Track Edition.

Aside from its beefed-up engine, reinforced body and firmer suspension, the Nismo model gets aerodynamic upgrades and distinctive interior trim.

The 2015 Nissan GT-R is powered by a turbocharged 3.8-liter V6 engine that generates 545 hp and 463 pound-feet of torque. A six-speed automated manual transmission routes this power to the ground through an advanced all-wheel-drive system.

Utilizing a built-in launch-control program, its performance is nothing less than jaw-dropping, with the 0-60-mph sprint taking just 3.2 seconds. This powertrain also achieves respectable fuel economy, with an EPA-estimated 19 mpg combined (16 city/23 highway). We validated these estimates with our own real-world 23 mpg measured over Edmunds' 120-mile evaluation loop.

The 2015 GT-R Nismo gets an upgraded version of this V6 that puts out 600 hp and 481 lb-ft.

Standard safety features on the Nissan GT-R include antilock disc brakes, stability control and traction control, front-seat side airbags and full-length side curtain airbags. In recent Edmunds brake testing, we recorded a best 60-0-mph stopping distance of 99 feet, which is on par with the world's best.

The most significant changes to the 2015 Nissan GT-R aren't readily apparent from the outside, but they're hard to miss once you're behind the steering wheel. Perhaps the most marked improvement is that Nissan's supercar now feels considerably more refined in everyday driving. In fact, the more compliant ride, lighter steering effort at low speeds and quieter interior put this latest GT-R on a stronger footing with more expensive rivals from European luxury brands.

Thankfully, these upgrades don't take away from the impressive performance that has made the GT-R the object of gearhead fantasies since its U.S. debut five years ago. In fact, testing the 2015 GT-R's handling on our slalom and skid pad exercises showed a measureable improvement over prior less compliant versions, setting a new production-car record in the process.

The turbo V6 produces acceleration that's not unlike the jump to warp speed, while the transmission rips off rapid and perfectly rev-matched gearchanges. The sophisticated all-wheel-drive system is still a wonder, too, as it directs power where it's most needed for maximum traction, and for greatest effect on handling.

This is also an exotic that remains remarkably easy to drive fast. Chuck the GT-R into a corner, any corner, and it sticks through the bend and rockets out the other side. But it never surprises. It's frightening in the same way that commercial air travel is: It's the conscious thought of the speed you're traveling (and the consequences thereof) that raises hairs, not the direct knowledge that you're in control of something special. Some drivers might find this advantageous, but others will bemoan the lack of passion.

The 2015 Nissan GT-R combines the driver-oriented cockpit you'd expect from a sport coupe with user-friendly controls. The combination of well-bolstered front seats and paddle shifters makes it easy for the driver to focus his or her attention on the business at hand. Everything is within reach and where it should be, just like in a normal car.

In addition to the typical navigation and audio displays, the 7-inch touchscreen can bring up info like gear position while underway and also play back a range of performance data including lap times and G-forces generated during aggressive cornering.

Unlike cars with similar performance, getting in and out of the upright GT-R is a snap. The seating position is relatively high and the doors are long. The standard front seats also offer surprisingly good comfort for such a performance-focused machine, making the GT-R a reasonable road trip companion. The Black Edition, Track Edition and new Nismo models all get more heavily bolstered front seats better suited to aggressive driving.

Rear seats are only suitable for small children but, in this category, that's more than can be said for many of its competitors. Trunk space is also decent by supercar standards, with 8.8 cubic feet of cargo room.