Possibly the noisiest city in China, which is saying something, and although not without its attractions, offers the least of the major metropolises for the effort put in. Even if this is your only chance to go to mainland China, there are other side-trips from Hong Kong more worth your time: Kaiping, for instance. But better, if you think you may one day return, to save your efforts for another longer trip in the future. I'd second the suggestion of Macau for now. No visa needed.