Unfortunately I don't know any good website which I can give you but I can share some of my opions and knowledge.
Unlike Americans, Europeans are very careful and critical comsumers in the sense that we are very careful with what we buy are usually compare and plan our expenditures. In order words we don't do a lot of impluse shopping and buy anything that comes our way and when it comes to expensive products we are even more careful. Many people here in Europe concider price value, functionality, quality build, mantainence cost and fuel consumption when they buy a car and if you objectiverly compare american cars with european ones, the europeans are in 98% of the cases more practical/functional, have better build quality, better exterior looks and lower fuel consumption.

The whole thing isn't really that complicated, the European automtive market is very competitive and if you want to successed you have to produce equally as good or even better cars than whats availible and in this case GM hasn't done that. One might argue that East Asian cars aren't as good as the German ones but they have done well in Europe. The difference between American and East Asian is that the Asians cars are signifigantly cheaper, reliable and have low fuel consumption.