Macau is an easy day trip from Hong Kong. I don’t think I would like it as a destination in itself. While it is famous for its gambling and casinos if that is not your focus, one day is more than enough.
The ferry leaves frequently from downtown Hong Kong. You can buy your tickets in advance or when you get there. If you buy them when you get there, I recommend giving yourself at least 30 minutes to make it to the dock. It is a long walk and you still need to go through immigration.
Also, unless traveling during peak times and the boats are full, if you arrive at the gate early, they will let you board an earlier ferry. We did this on the return trip.
There are two ferry terminals in Macau, the Outer Ferry Terminal and the Taipa ferry terminal. We arrived and departed from different terminals which saved us a little time and money. I recommend arriving at Taipa where you can catch a free casino shuttle to one of the hotels to see the strip, get some cash etc…
From there we took a taxi to Coloane village for a famous egg tart and to walk around before proceeding to the center of Macau to see Fortaleza da Guia; Senado Square and the Ruins of St. Paul. I was extremely impressed with the Ruins of St Paul and that alone made the day worth it.
Little known fact is the first scenes in Shanghai of Indian Jones and the Temple of Doom were filmed in a nearby alley, Avenida de Almeida Ribeiro.
We were there on a Monday so we weren’t able to see the Pandas. But I would like to see them on my next trip.