All cars are looking more and more alike between brands/platforms because of the tightening of economy and carbon ratings. There is only so many ways you can cut through the air efficiently.
As for the Mustang and Aston Martin comparisons versus the Mustang being a muscle car, well, yeah, Astons are muscle cars too. In fact I'd argue the Europeans (Aston, Mercedes, BMW) have been making the best modern muscle cars for the last decade or so and it's about time Ford got in the game in a real way. I won't speak to the ChryCo and GM cars since I think they really suck compared to their European rivals.
Additionally, compare a 1970s Aston to a first gen Mustang. They are very similar looking. So Aston "copied" Ford, Ford bought and sold Aston, and now Ford is copying Aston. They aren't direct copies and the shapes are awesome so I don't have a problem with it.
Compare a Ford Explorer to a Land Rover Evoque or Range Rover lately? Ford used to own them too.
If the new Mustang is as good as the hype is suggesting I can see a lot of people going that route instead of the European cars.
Personally, I'm on the fence between doing an old school restomod (why I'm at this forum) versus just buying a new Mustang or BMW M3/4 when it comes out. As awesome as the new C7 is... I don't think I can be a Vette guy.
Classic Mustangs have a certain simple "Zen" to them. They have enough aftermarket support to be turned into a road course terror. That is why I seriously flirt with the idea of a Fox notch or a `60s Mustang for my next car build versus "turn-key". Other options include getting back into a 911 or S2000 or something more track focused of that nature.
My take on the new Mustang:
The C-pillar shape and rear window shape goes right back to the delicacy of the 1965 fastback. Love it! That said, the roof line drops a little too fast and is very reminiscent of the 370 and others. See the aero point up above. I'd have preferred a roof line like the 1965 (i.e. similar to the classic Porsche 911).
The Dash. In the lower spec cars the expanse of plastic in the middle is a lighter colour and reminds me of the cockpit of Thunderbird 1 or something along those lines. Not a big fan of that. But, in the GT spec the center is a darker colour and it really looks good IMO.
Really like the lit marker slits in the grille that go back to the 1964 cars.
The rear tail light assemblies are really busy. While I love the complexity of the shapes/form here I keep wondering how much of a pain in the a55 it'll be to clean on car wash day.
Really happy they got rid of the cheesy retro font on the instrumentation.
I really hope the steering wheel feels better than the wheel in the current car. It sucked. I also hope the quality of the plastics used in the interior is better than the previous cars. The plastics in the previous cars were hilariously bad.
2¢