I've been to Thailand, Hong Kong (before the changeover), and Japan. It was when I was fairly young through, so my memory is a little foggy of a lot of it.
Thailand was really different. The traffic (and especially taxi drivers) are insane. Ours was going up to 140 kph in fairly dense traffic (actually caught a little air once or twice). Scared the crap out of us. I remember seeing one of the "touristy" things with crocodile shows, and performers sticking their heads in their mouths. Apparently every once in a while, it doesn't end so well, but no one lost any body parts when we were there. The other thing I remember was the pollution. If you spit, it was literally black.
Hong Kong was pretty cool. Very modern (cutting edge even) and clean. Even cheap accommodations were almost luxury compared to here. Got to ride one of the trains and see a bunch of the countryside. Really enjoyed it there. Dunno if it's as nice now.
I don't remember much about Japan, other than how crowded and expensive it was.