The seven-speed automatic transmission that’s offered across the M-Class line earns high marks from reviewers. Adding to the M-Class's performance credentials are superb brakes and an adaptive damping system that improves stability and minimizes body roll during turns.
Mercedes-Benz sets the diesel performance benchmark with its new BlueTEC engine technology, but the V-6 doesn’t provide the urgency reviewers want. Regarding the ML320, Edmunds says “there's an exasperating delay when you floor the throttle from a stop or forward creep, as though the transmission has been caught off-guard. Forget Mercedes' claim on its Web site of ‘V8 power in a V6 configuration.’ Thanks in part to this conservative shift logic, the ML320 Bluetec would have its hands full keeping up with an ML350 and its gasoline-powered V6.” Motor Trend notes that, at speed, “Downshifts are quick and smooth. Put your foot to the floor and there is little hesitation, as the torque is strong enough to pull the SUV like a performance coupe through the powerband.” Additionally, “With 398 lb-ft of torque at 1400 rpm (210 hp at 3800 rpm), the engine is comfortable staying at 1800 rpm; no matter the hilly conditions, the engine has pulling power.” MotherProof comments, “This diesel is touchy and uppity. It takes some time to figure out how to finesse it because it’s pretty hyper. I was snapping everyone’s heads around for a day or so until I got used to it. Technically it’s called torque, but I call it herky-jerky.”
MyRide.com sums up the 2009 ML320: “The rest of the driving experience is just like driving a non-diesel M-Class. Ride and handling are tuned to a better-than-SUV balance, with just a little body roll a good dose of on-road stability. The brakes deserve extra credit for their surefooted feel and performance. And the interior is luxury quiet, with none of the diesel tick getting into the cabin.”
The V-8-based ML550 generates 382 hp and has no problem getting the most from each and every one of them. Car and Driver finds the ML550 "to be seriously quick, hitting 60 from a standstill in 5.4 seconds." This version gets 13/18 mpg. The top-end ML63 AMG with its hand-built 503-horsepower engine defies all established SUV speed conventions. ForbesAutos raves about the ML63's "blistering straight-line speed" and notes that the "hand-built engine spurs the big Benz to 120 or 130 mph with ridiculous ease." Its 11/14 mpg fuel economy is unapologetic.
Though some reviewers clearly feel that the V-6 ML350 requires too much of a compromise, Kelley Blue Book differs, stating that "opting for the lower-priced, higher-mileage ML 350 won't leave you feeling short-changed in the power department."