I've been to Hong Kong a half-dozen times and don't feel remotely close to having seen or done the city. The more I discover, the more I find that there is to discover. (Your mileage may of course vary. A place either speaks to you or it doesn't.)

That said, Hong Kong is an exceptionally intense city. It is always in motion, and every block arouses all of your senses. It's an endless stream of people, sights, smells, sounds. On my first trip, I started to feel totally overwhelmed after about 4 days.