The previous-generation Infiniti M arrived with V8 power in 2003 ready to do battle in the highly competitive midsize luxury sport sedan class. But conservative styling and a lack of interior room hurt the car's appeal. To address this situation, Infiniti released the redesigned M45 three years later. A larger and much more stylish design, the M series (there's also a V6-powered M35) now competes more broadly and successfully against its Japanese and European rivals.

Now, a few years on, the 2008 Infiniti M45 continues to be a standout in terms of performance and cabin space, and has won wide critical acclaim. This year, the M45 receives all-wheel-drive availability for the first time. Similar to the AWD system on the M35 and FX crossover, the M45x AWD has a normal 50/50 torque split and can apply up to 100 percent of engine power to the rear wheels when needed. Other notable changes this year include revised exterior styling, new interior trim pieces and an upgraded Infiniti navigation system with real-time traffic and hard drive-based digital music storage and playback.

Overall, the M45 continues to be a great choice in the performance-oriented luxury sedan segment. Of course, the M45's main rival for sport-oriented shoppers is BMW's freshened and more powerful 5 Series. Those with bigger pocketbooks and a keener eye for comfort-focused luxury might be more pleased overall with the segment standard Mercedes-Benz E550. Also, the V6-powered M35 could save you money while providing similar features and more than enough power for most buyers. But for all-around competence in a generously equipped and fine-performing luxury sport sedan at this price point, it's hard to find fault with the 2008 Infiniti M45.

The 2008 Infiniti M45 is a midsize luxury sport sedan offered in two fully equipped trim levels: base and x AWD. The standard rear-drive M45 comes with 18-inch alloy wheels, adaptive xenon headlights, leather upholstery, 10-way power and climate-controlled front seats, dual-zone automatic climate control, wood accents, an auto-dimming rearview mirror, a sunroof and Bluetooth. A six-speaker audio system with a six-CD/MP3 changer, satellite radio and an auxiliary audio jack is also standard. The M45x AWD comes with all-wheel drive, of course, and is slightly different in terms of standard and optional feature availability. For rear-drive M45s only, the Sport Package adds rear active steering, a sport-tuned suspension, 19-inch wheels, high-performance tires, a sport steering wheel and different interior trim and seats.

Other optional packages pile on more technology and luxury with amenities. The Technology Package includes an eight-speaker Bose audio system with a dedicated iPod interface and a hard drive-based navigation system with digital music storage, voice recognition, real-time traffic and a rearview camera. On top of that, the Advanced Technology Package adds a 14-speaker surround-sound Bose audio system, adaptive cruise control and additional safety features. The top-shelf Premium Package includes both technology packages and also adds power reclining and heated rear seats, rear audio controls, a rear sunshade and an entertainment system.

The M45 features a 4.5-liter V8 that generates 325 horsepower and 336 pound-feet of torque. A five-speed transmission with manual shift control and downshift rev-matching transmits power to the rear wheels, or to all four wheels on all-wheel-drive models. In past testing, we hustled an M45 to 60 mph in only 5.7 seconds. EPA-estimated fuel economy for 2008 is competitive with its rivals at 16 mpg city and 21 mpg highway for rear-drive models. AWD models have a 14/20 mpg rating.

The 2008 Infiniti M45 includes standard antilock disc brakes with brake assist, stability control, traction control, front-seat side airbags, full-length head curtain airbags and active front head restraints. An available advanced lane departure warning system alerts the driver of unintended lane drifting and, if necessary, automatically applies slight brake pressure to the wheels opposite the side of departure direction to help prevent the M from inadvertently drifting out of its intended lane. In Insurance Institute for Highway Safety crash testing, the M45 scored a top-ranked "Good" rating for both frontal-offset and side impact protection.

The V8-equipped 2008 Infiniti M45 offers plenty of torque, with smooth and abundant power delivery around town or on the highway. The firmly calibrated suspension provides a fine balance between ride and handling qualities, and the M also exhibits impressive braking performance and steering response. Although we generally find it to our liking, consumers with a luxury bias may find the steering and suspension feedback a bit harsh around town and over uneven pavement, especially in extra-firm Sport Package models.

The Infiniti M45's large cabin seats five comfortably and is well appointed with leather trim and standard rosewood accents. Its seats are firm, highly adjustable and comfortably bolstered, even in non-Sport Package vehicles. While past models weren't quite as elegant and thoughtfully refined as others in its class, the 2008 M features new electroluminescent gauges with "gear-like" detailing, a revised center console, updated trim and new color options that should help it better compete against even luxury-oriented rivals.

Shoppers focused on the sport side of the equation will feel right at home with the M's simple layout, especially in Sport Package-equipped models with their unique steering wheel and shifter stitching, exclusive front sport seats, aluminum cabin accents and bright-trimmed pedals. The layout of the center stack controls still isn't as clean and intuitive as we'd like; however, it is still friendlier than some of its German competitors' point-and-click interfaces.