I work directly for Great Wall Airlines on the B744 and really have no serious complaints. We get paid what they said we would. There are bonuses that I did receive. The housing allowance is excellent, as is the school allowance (albeit only for one kid). I don't live here but commute from Auckland, but another Kiwi did move his family up here and they are enjoying themselves.
We are out of Shanghai, so I can't speak for Shenzen. We are also half owned by SQ and have excellent management as far as that goes (all my opinion). I have heard nothing but troubling thing's out of any of the Hainan Group airlines, so you might want to get a bite out of someone who works for Hainan/Yangtze River/Hong Kong Express etc.
Any other questions regarding China you can go ahead and PM me. We are definitely looking for pilots. We left a B767 worth of freight on the ramp today and I'm running a full hour roster, with home leave (closing on 100 hours for the October roster).
Good luck with it whatever you do.