I picked up this game after cancelling another preorder and I'm delighted I did so. Hong Kong looks fantastic, the story is solid, it's pretty addictive and the combat is deeply satisfying. Like leemond, though, I have a feeling the story can be rushed through pretty quickly so I'm hanging back and spreading myself over a bunch of side activities. Also there are some teething problems with the PC version they need to sort out, mostly down to dodgy camera while driving.
I haven't found much use for guns yet. In fact of all the game mechanics, the gunplay alone feels kind of janky. I've found a couple of guns in lockboxes but finding them didn't end well for me. When I found the second one I thought it would be a great idea to massacre one of the unarmed hacking-site gangs with it - that just made everything way harder than it had to be, since the police started on me for the very first time outside of a mission or hijack. I had to run off, come back and reattempt it bare handed. TBH that suits me fine because I'm having way too much fun beating the crap out of triads with my bare hands, in ridiculously brutal ways.