The Hong Kong arrival isn't always spectaular now (certainly not like the old Kai Tak one). It depends which direction they are using the runways.

If you are landing on 05 (i.e. towards the east) then there is very little to see as you come in because your approach is over the Pearl River estuary to the west of HK.

If you are landing in the opposite direction (i.e. 23 towards the west) then you may get a good view of HK on the approach primarily from the left side (A seat) depending on the weather.

I'm less certain about Sydney - I have been there a few times and recall that you got views of the city both sides because we flew past the airport over the sea (with the city on the left side) then did a 180 and approached with the city on the right side. Someone more regular there may be able to correct me.