My 2 cents worth and some background that might help...
I left the UK in my late 20's to go to Malaysia as an expat in circumstances that sound very similar to what you describe. I HATED it with a passion. At the time, I would have given you a list of reasons I hated it that included: heat, sanitation, impossible to get anything does/locals are lazy and lie to you/don't do what they say they will, nothing to do, nobody speaks english etc etc. KL was (at that time) alot less developed than it is now and alot less developed than Hong Kong. Since then I have lived in both Aus and NZ and now HK.
However, the insights I have gained by moving around these various countries are that enjoying a move often has alot less to do with where you move and what you find there, than what you bring with you (and I'm not talking about possessions here!). If the person I am now moved to the KL as it was then back in time, I would enjoy it (I think). The place would not have changed but I have.
So - the question for you is not "what is HK like" but "what am I like?". The others above have given you a big picture of HK ... but who are you? How do you feel when you are out of your depth? When you are lost and cannot read the sign posts? When you ask (in a shop, restaurant, on the street) for help and people either ignore you or answer in a way you cannot understand? Do you smile and try again, relaxed. Or do you get upset and scared or angry?
Have you spent much time in a foreign place? Do you care about eating exactly the right foods, same brands, same time of day, cooked by yourself in a large kitchen with an oven? Or are you keen to get out, try new stuff, live in a tiny place where you probably cannot cook much?
How do you deal with heat and humidity? Does it upset you or stress you? Or is it just something you deal with?
How much do you need your family? Are you close? Dinners on Sunday and on the phone most days? Or "family"? I see them at xmas only! Ditto friends. In other words, even if HK is fabulous, are you really going to miss people back home?
Re work - what will your job involve? Is it just the same as it would be back home (dealing with overseas, or expats in your firm) or will you have to market to locals (or other asians) and work with, work for, or be the boss of, locals? If yes, have you done this before? If not, you might encounter some significant culture shocks!
When do you work best? At 8am in the morning? Or are you a night owl? A night owl might fit the local culture better than a morning person (particularly if you have a local boss who thinks that people staying late is a good thing!).
These are some things to think about. I love HK. When I agreed to move here, I expected to hate it. But if you let it, it can really grow on you. If you leave your baggage behind you can have a great time - but you really, really need to be open minded and flexible. And only you know whether you are or not! Even if not, it'll be a great way to develop yourself, just don't expect to enjoy the experience at first....