I visited Nairobi National Park with my girlfriend and her best buddy on the 8th of January 2013. I couldn't believe it! The camp is well-ordered with good trails and way posts, it is also patrolled by friendly and helpful rangers of the Kenya Wildlife Service.
The best bit is seeing big game such as Cape Buffalo and Rhino (white and black) against the backdrop of Nairobi city. The amount and variety of game is simply amazing, the fact that it is literally on the edge of a large densely populated city makes it stunning.