I've owned 2 American cars in the last 15 years . . . one crap, one good. We have a Maxima and a Camry now, both good.
Why they failed:
1. The only "good" vehicles they made were high end gas guzzling pickups and full sized SUV's, and cool but impractical vehicles like the Corvette and to a lesser extent the Mustang. The only original interesting sedan was the Chrysler 300 and it gets severe mark downs for quality issues. Cadillac is finally getting a clue.
2. Completely lost out in the mid-sized sedan market. Ford utterly blew it with the 500 and the Taurus, GM foisted that joke the new Impala on the market, and Chrysler as stated had a unique car in the 300 but crap build, and the Charger is interesting but red neck ish. Ford is finally going to come out with a new Taurus that even they admit is the car they "should" have built 3 years ago.
GM has too much cross product line duplication . . .if someone doesn't like the GMC Acadia, they're likely not going to like the Chevy Traverse or the Saturn Version of the same car. GM needs to cut Pontiac, cut Buick and cut Saturn, and have just Chevy for "lower end" cars/trucks/suv's and Cadillac. Ford needs to cut Mercury. Chrysler needs to pair down its offerings as well.
IMO the only one of the 3 that has any consistant quality control is Ford . . . Ford may actually make it if they cut Mercury, and get retooled sedans that people want on the road.