DX:HR had enough story, gameplay and player choices to actually keep me happy. It's like they did spend enough time either making a good game, or keeping what made the original engaging. Unlike some other games (Crysis 2 IMO and especially Far Cry 2) which just try to run off the good will from the previous game and then offer a COD or sub par gameplay. Don't get me wrong, Crysis 2 had the potential, but I feel they missed it. With DX:HR I think they did enough story, enough choices etc to keep the game "fun" and engaging and entertaining.
PS, AFAIK they main reason for going back to "china" was a limit in time and budget on the level design. They wanted the upstairs bit of China to be (while the same continent/city) and entirely separate and different level. But they had to cut back and reuse the same one over. You get a glimpse of it out the window at the skyline. All green parks and white buildings.