I think the second half of the next century will indeed be one in which China will start playing a dominant role. But I more or less agree with Keltoi on this, unlike the British or Ottoman hegemony, American absolute power is unlikely to decline, but rather it's relative power will as others get richer. There will be no collapse, like the British Empire or the Ottoman Empire collapsed and splintered. America will remain rich and China will gain the importance it really deserves.
I noticed something else that was interesting about China though. Modern Chinese city life resembles that in the West very much. I mean, to put it crudely, it appears materialistic, individualistic and pretty much void of spirituality and religion. IMHO this means that what is nowadays perceived as Western culture isn't really Western, or based on the Christian heritage, but rather a result of economic prosperity, ie. modernity. This is a positive development, since I believe it will be more likely that the West and the East will not have this huge cultural barrier that separates them. It will make it easier to work together and peacefully coexist in the future.