To what extent does Paine's characterization of America in Rights of Man still hold true today? How can I write an essay on this?

The best way to approach this essay is to define the key components of Paine's characterization of America. How does he describe the United States in Rights of Man, published in 1791?
The next part is going to depend on your own viewpoint about the state of our country in the present day. You'll have to ask yourself about each of the components that Paine lays out, then decide for yourself whether or not you think that parts of his description still hold true today.
Let's pin down a few facts right off the bat. Paine was born in England, but he supported American independence from England. He was also a supporter of the French Revolution. In Rights of Man, he discusses both of these topics. Keep in mind that the United States was a brand-new country at the time, and it was founded, to some extent, on ideals. 
Could we describe Paine's depiction of the US, then, as idealistic? Indeed, some scholars would go even further, describing his vision of America as utopian. Consider the following passage from Rights of Man:

If there is a country in the world where concord, according to common calculation, would be least expected, it is America. Made up as it is of people from different nations, accustomed to different forms and habits of government, speaking different languages, and more different in their modes of worship, it would appear that the union of such a people was impracticable; but by the simple operation of constructing government on the principles of society and the rights of man, every difficulty retires, and all the parts are brought into cordial unison. There the poor are not oppressed, the rich are not privileged. Industry is not mortified by the splendid extravagance of a court rioting at its expense. Their taxes are few, because their government is just: and as there is nothing to render them wretched, there is nothing to engender riots and tumults.

Let's go through a few of these points as prompts for your essay. Is America still made up of people from many nations who practice different religions and speak different languages? The answer is yes, of course. 
What about the poor not being oppressed, or the rich not being privileged? I doubt you'd agree with that. I'd suggest scanning recent news articles for examples of policies or decisions that seem to favor the rich over the poor.
Which brings us to the next point. I don't know what your personal politics are: this essay is yours, and you'll have to respond according to what you believe. But the notion that nothing could "engender riots and tumults" seems like the exact opposite of the America we're living in today, and I encourage you to use this as a basis for arguing that Paine's characterization of the US is idealistic at best.