I recommend the parks (Grand Canyon not so much if you like hiking), but not the cities. Los Angeles, a thriving city of thirteen million people who can't afford to live there, is a wasteland, oddly like a field full of boxes pretending to be a city. Las Vegas is the worst place I've ever visited in my life. And finally, I never really appreciated being able to buy fresh fruits and vegetables until I spent a month in the nutritional wasteland that is United States of American. But those national parks... they are worth it.