Yeah, New Year (Jan 1) is massive here in HK.
Lot's of partying and a big fireworks display in the harbour at midnight. It's a public holiday here so banks and government offices will be closed but nearly everything else stays open.
Christmas day is the same with most things open. Christmas will be very busy though as most locals don't celebrate Christmas but have the public holiday on the 25th.
Here in HK most chain stores and sites stay open over CNY too. But it is noticeably quieter and many/ most local shops and restaurants will close. Some for a day and some for the whole holiday.
Going to the Mainland or Vietnam is more like visiting Atlanta on Christmas Day - everything is closed!