I've never been to Singapore so I can only vent about Hong Kong, it's a good vent though.
I only spent 3 days in Hong Kong, I had 1 layover when I flew to Australia, and another layover (on my way back to Europe) where I booked one night after falling in love with the city on the first layover.
From all the big cities I have visited, Hong Kong may very well be the most interesting citiy I have ever been to, where I could feel like a proper traveller again. Cities like New York may be nice, but they have the definite advantage of the North American entertainment industry which is the world wide monopole. A lot of those cities desirability come from having seen those cities in movies, music videos, shows etc. throughout your life from the moment you could open your eyes. Hong Kong does not have this from a westerners pov, except if you watched Jackie Chan movies like crazy. But Hong Kong did not seem isolated or small in anyway, it was quite the opposite. Hong Kong felt like the asian counterpart to New York, home of the big banks and global players.
Hong Kong gave me the feeling of exploring again. Foreign characters everywhere (even though most was translated in english) and completely different looking people. But to be honest, I can't really say if one couldn't say this for every other country that is not based on christian heritage or adapted it. I do not remember how I felt when I visited african cities. Most of the countries I visitted when I grew "fully" conscious were christian or at least western based countries.