It's nice. Sexy and less boxy.
But, the trapezoidal grill shape seems to be a take off of the Ford Fusion grill shape. It's not bad, but it goes away from the more recognizeable rectangular grill.
Roof line from the A-pillar to the rear looks like they plain old stole it from a Nissan 370Z.
Headlamp assemblies look very modern, but there's no resemblance to any prior version of the Mustang.
Rear quarter panels look Chevy Camaro-ish.
Tail-lamps and center section between them looks really good. Going away from that center circle trunk emblem thingy was a good thing.
Front quarter panels to doors and the creases look nice and smooth. No non-functional air vents, which I've always hated.
Bulge on the hood is nice, no homo.
No spoiler on the rear hatch is nice. Very clean but allows someone to add one later, or it can become an option for a higher-end model.
The lower diffuser below the rear bumper is a nice touch.
Other than that, the non-solid rear axle is a new thing which I think is a step in the right direction too.
The three engine option isn't good. They should get rid of the V6 as the standard and just offer the V8 and turbo inline-4 as the standard. I'm guessing they want to milk as much cash out of the existing V6 engine as possible.