American cottage cheese is usually more watery and more mild in flavor than traditional ricotta. A good example is lasagna. If you try to substitute cottage cheese for ricotta on an equal basis the lasagna will probably be runny and it won't taste as good.
It depends if the ricotta is drained or not. Some undrained ricotta is runnier than a lot of cottage cheeses, but you are right they are definitely more 'watery' in flavour.
I do feel that you can use cottage cheese instead of ricotta but I wouldn't even call it a substitute, the dish would be completely different. I have used it when I didn't have any ricotta and the inspiration to cook a dish with ricotta has come to late in the day to go pick some up (dislike supermarket stuff, I buy straight from an Italian manufacturer).