Hong Kong is quite small, in two days you have seen the most of the city.
If you have an extra day I highly recommend to go to Macau.
Full of casinos, from the main Las Vegas casinos to the 70's chinese ones... it really worth the visit.
You can take a ferry from Hong Kong that takes you there in 1 hour. There's one each 15 minutes / 24 hours. About 170HKS (17€) per person one way