What has happened to me is that I thought it would be possible to choose from all the courses in the catalog. When I got here, only 8 of them were offered, and 1 of these was what I wanted to do. Also, students already at a university can pre-register, so check that the courses you want to do are not full. You can be prevented from doing a course for no other reason than that it is full, that the computer processed other names before yours, and this can be frustrating. On the plus side after all those caveats, if you are someone who genuinely loves your subject, I think you will find America an exciting place to study.
People seem more openly intellectually committed, more honest about their desire to work hard.
Lastly, try to end up in a university in a place that interests you. DC is uniquely situated between the North and the South and provides a fascinating perspective on both. If you are an American culture junkie, as I am, you might want to be in somewhere that doesn't just exist for its university. Washington is amazing because there are so many different kinds of things happening here at once. Build that in to your planning.