Part of the problem with the Fox body Mustangs of the eighties and early nineties was the hatchback configuration. The fastback coupes that followed (I had a 2000 and currently have a 2011) do not have (in my experience) the creaks, rattles, and shakes that the hatchbacks had (I also had a Fox body Mercury Capri).
Yes, it's true that the pushrod Windsor V-8s were low in horsepower (peaking at 225 from 1987 to 1991), but they also had 300 lb-ft torque, all available at a fairly low rpm compared to the OHC Modular engines, so they weren't lacking in every-day driving power. Top speed, 0-to-60, or quarter mile times doesn't matter for most people, 30-70 times merging onto the highway is probably the most important performance factor in automobiles.
My 2011 V-6 has 305 hp, which is plenty by most people's standards, but it doesn't feel like that much. I've driven many pushrod V-8s with less hp, and they would have probably been better merging than my OHC Stang because of the full torque being available at a lower rpm. It also doesn't really take off until I reach highway speed, with 0-60 being about average, but then once I'm there, it gets up to 90 in the blink of an eye if you're not careful.
Someone earlier in this thread complained about the transmission (automatic, I assume) on Mustangs. Mine seems like it has a little difficulty staying at 6th gear (Overdrive) unless it is in cruise control, and seems to slip back and forth between 5th and 6th. It's just a minor annoyance, since I normally use cruise for highway driving anyway. I think that 90% of Mustang (and Camaro, Challenger buyers) buy these cars for the styling, and they aren't going to use the backseat for anything but their coats or briefcases/backpacks anyway. Performance isn't that much of a factor in their decision to buy these cars.
I just read an article in C** And Dr**** (not sure if we're allowed to use magazine names here) that totally trashes the EcoBoost 4-cylinder. Ford is forcing it on people by making the V-6 only available in Spartan, entry-level Mustangs with no options. Despite having 10 fewer horsepower (which might be a marketing ploy and not really accurate), the six still outperforms the four in just about every performance measurement, and the savings in mileage isn't as good as it was supposed to be. Plus, you'll probably have to replace your exhaust manifolds in 50,000 miles, like people who bought the EcoBoost six in F-series pickups instead of the Coyote V-8 are finding out.
While I don't want to eliminate the EPA or anything like that, I do believe that CAFE is killing the automobile industry. Gas is expensive in the U.S., but nothing like it is in Europe, where it costs about four times as much as it does here, once the gallon to liter and dollar to euro conversions are made. Ford was unable to offer an automatic in their Shelby and Boss 302 Mustangs because they would have sold too many and it would have hurt their CAFE numbers (although not too many people would have probably bought automatic Boss 302s, but the sixties Shelbys were always available with autos). And other than the low-volume supercharged 6.2L in the Cadillac CTS, the regular LS3 engine was never available in the midline CTS (where most people would have probably chosen it if it were an option) or the RWD STS (which would have been an improvement from the mediocre optional Northstar) from the mid-2000s, probably because they would have sold too many. I don't know how Chrysler isn't getting killed by the government because they don't sell a lot of Darts and 200s, and are still able to sell SRT 6.4s and single-digit-city mileage 707 hp Hellcats, even in tiny numbers.
Ford really screwed up with their EcoBoost program, whereas GM and Chrysler were smarter developing cylinder deactivation technology and beating Ford with eight-speed automatics compared to Ford's six-speeds. The EcoBoost engines, with the exception of the 3.5L six (in the Taurus SHO and Lincolns, anyway) aren't particularly powerful and the mileage has been mostly less than expected.