Anyone can visit North Korea as a tourist. However, being a citizen of either South Korea or the US makes it a lot harder. Visa applications made by citizens from these 2 countries have a high chance of being denied. So it's not exactly a "handful" of people who've visited the country.
That being said, you will need to apply for a visa through certain travel agencies. You can find a list of them here: http://wikitravel.org/en/North_Korea.
And yes, as a tourist, you will be closely watched by your North Korean guide/minder. You will not be allowed to wander off on your own without your minder following you. Instead, there will be guided tours planned out for you.
On the bright side however, tourism there is very "safe", in a sense that crime rates are extremely low, considering the consequences one might face committing any crimes.
So long as you don't do anything stupid like spit at a statue/picture of the Kim family, openly criticize the government, you're pretty much safe. Don't worry too much about getting sent to a prison camp there. The North korean government wouldn't harm you considering the repercussions they'd occur from your respective government(unless you're South Korean).