I went to an American Chinese restaurant with my SO who is Chinese. She wouldn't even touch the food. There was a proper mainlander there. We discussed the food, and he said in Chinese "You'll never find this food in China", which manages to be a fantastic back-hand of a compliment.
American Chinese food is basically all the flavours and none of the substance, like eat a lasagne with no vegetables or pasta; it's similar, but you're really not getting the proper thing.
That said, I rather liked the overly sweet and sugary Chinese food in America, it's like candy.
EDIT: It could be a lot worse.
In Paris, because they think good food means having crap portions and no flavours, all the food (even the Asian ones) are hugely deflavoured because a strong flavour may harm the Parisian.
At least American food tastes of something. Parisian food is a massive let down in regards to their Asian foods, especially Korean which seems all the rage.
MORE EDIT: The best two provinces for Chinese food, in my opinion, are Szechuan and Hong Kong. Hong Kong makes what every other country thinks Chinese food is, and Szechuan makes the spicy, amazing dishes that can make you melt in happiness. Go find a Chinese Hot Pot, get some peanut sauce (you can make your own with peanut butter and vinegar), get some beef and chow down on that shit. So good!
EDIT 3- THE EDITING: That said, one thing that I find aggressively bad is the massive mark-up in price. For £8, I can field 3 massive dishes of Canton food with drink and rice with a friend and take half of it home for later.
In the U.K., it would cost £30, you would get half as much, and it would be so much worse quality. A massive plate of sweet and sour chicken is about £3 here, it is easily £7 in the U.K.
Can't eat Chinese food when I return anymore