Unquestionably the star of the show, Mercedes' new 3.0-liter, twin-turbo V6 is a hoot. More than any other piece of this car, it feels like a true product of AMG. It revs fast and fierce to its 6,500-rpm redline, and sounds damn good along the way, thanks to the AMG performance exhaust. And with all 384 pound-feet of torque on offer between 2,000 and 4,200 rpm, it always feels like the punch you're asking for is readily available.

Mercedes went far enough with the C450's engine, but it didn't with the transmission; the C450 uses Merc's long-serving 7G-Tronic automatic. It's fine if you leave it in full automatic and the drivetrain in Comfort. It's less fine if you switch to Sport or Sport+. And it's really not fine at all if you select the full manual mode. It's quick on wide-open-throttle upshifts and other aggressive situations, but it stumbles on downshifts. We found ourselves clicking the left paddle two or three times trying to force the seven-speed automatic to drop down. It was similarly fickle around town, where the gearbox just wasn't keen on shifting up.

The polar opposite to the mainstream transmission is the C450's suspension. Multi-link arrangements sit fore and aft and are paired with standard three-mode adaptive dampers plucked directly from the C63 AMG. They're firm in their sharpest mode, offering up precise, sports-sedan-worthy reflexes and reactions to steering inputs without being punishing over Michigan's third-world roads. Left in their softest mode, though, the ride is scarcely less comfortable than a C300 with the Sport Pack.

The steering also came up for special praise. It's fast, precise, and wonderfully weighted without feeling taxing or difficult at lower speeds. What's impressive, though, is how good the steering feels in its lightest mode. From on-center through to full lock, the weight builds consistently and naturally. It's easy to forget this is an electric steering rack. Feedback is strong, too, so you're never left guessing what the front wheels are doing. We also enjoyed the standard AMG steering wheel, and didn't really see the need for the optional Alcantara tiller.

Prices for the C450 AMG start at $51,725, including $925 in destination charges. We'd describe our tester as popularly equipped. It lacked performance-minded options like the $2,500 AMG Performance Seats, carbon-fiber trim pieces, and upgraded steering wheel, but had virtually every convenience feature. Boxes ticked include the Driver Assistance Pack ($2,250), the Hands-Free Access Pack ($250), the Multimedia Pack ($2,230), the Lighting Pack ($800), the Premium Pack ($1,520), heated seats ($580), 19-inch AMG wheels ($850), an excellent head-up display ($990), front and rear parking sensors with active parking ($970), and a rear-view camera ($460). Finally, there's that absolutely beautiful Cardinal Red Designo paint, which costs $1,080, bringing the as-tested price to $65,005.

When it comes to performance cars, we admire Audi's template. There's a basic model, then an S, and if applicable, an RS at the top of the range. Each vehicle has exponentially better dynamics than its lesser sibling, so that there's no confusing the driving experience of an A5 with that of an S5 or an RS 5 . Same with the A7 S7 , and RS 7 BMW has tried to replicate this formula with cars like the 135is and 335is , and more recently, the new M235i and X4 M40i. Mercedes ' analog is the new (stillborn) AMG Sport line, and this C450 AMG 4Matic challenger to Audi's S4 . It's got the right credentials – AMG's brand cache is backed up by a twin-turbo V6, a tweaked 4Matic all-wheel-drive system that sends two-thirds of its power to the rear axle, a sportier aesthetic, and sharper, more precise reflexes. But what a car like this needs is verve and drama. It has to make you want to drive it hard. With the C450, a week behind the wheel showed off stellar driving dynamics, but its character is too cool and businesslike – this is more C300 than C63 The C-Class range runs the emotional gamut. The C300 is pinned down and businesslike. The C63 is wild and emotional and makes you feel like a well-heeled hooligan. More importantly, it has an intangible something that makes you want to push harder and faster – it's what we expect from AMG these days, and the C450 just doesn't quite have it. Yes, we're getting used to this "AMG Lite" package, but until Mercedes can distill, bottle, and inject some more of that C63-ness into the C450 – or C43, as it'll soon be known - it's a hard vehicle to get wrapped up in.