I know this question is dated thus likely the OP Artem has finished his/her Postdoc contract long ago. But I will leave some comments as well, as a westerner (from a 3rd world country, engaged to a foreigner) finishing a 2-year-old postdoc contract in South of China.
Rebbeca's answer above is quite complete and fills most of the points, however some aspects may change depending on the local institution traditions and the candidate's background. This is why I emphasised the where I am in China and the fact that I come from a western 3rd world country, along with marital status.
Pros: China has great food, fantastic scenery, rich and deep culture and knowledge. Thus life in China will be anything but blend. Still nowadays a foreigner attracts considerable attention and interest, thus there will always be someone willing to help and get friendly. Academics are very respected in Asia, thus a postdoc should expect cordiality and polite treatment essentially everywhere. Criminality is almost zeroed, especially against foreigners. Stealing is rare, and people are relaxed about taking care of their belongings. In spite of officially a dictatorship there is a lot of individual freedom in China, as long as one is no activist. Likely the greatest positive aspect for a postdoc, getting a job in China is currently quite easy for anyone willing to embrace the culture, particularly open-minded foreign PhDs.
Cons: Local culture is not open nor flexible, meaning you are expected to accept local ways all times and gradually conform to or adopt the Chinese way of life. This tends to overwhelm foreigners so that most end up living in an expat bubble and eventually leave. As mentioned, salaries are usually lower and quite often there is a catch behind salary discounts. Communication is a major issue not only because of language barrier but actually mainly because most people in Mainland China imply statements and suggest contexts instead of uttering their minds directly. Assertiveness is often perceived as arrogance and blunt statements can easily offend. Because of their unique and inbred culture, Chinese nationals get easily offended (people say they are "glass-hearted") and in the counterpart cannot understand/accept what could offend a foreigner. There is a strict hierarchy in almost any form of communication which is hard to abide to as a foreigner with a democratic mindset. Scamming and lying are quite common and culturally acceptable depending on the context (meaning quite often others will not have you complaining about it). Face and clan cultures are not easy for just everyone to swallow. Local work culture pressures on posing all times, thus locals will pretend to work literally everyday from early morning into the night, and will post hardworking-related status updates on social media... even if they do not really work much. The internet feels like Truman's Show and workarounds are unstable, troublesome, and expensive.
I will quickly summarise what makes me very happy in China and what drives me nuts.
I feel in heaven while eating and shopping as prices are low, variety skyrockets, and quality is overall quite good. I feel physically safe at all times as long as I am wary of where I thread. Finding solitude isn't hard and I can have a mind of my own. Nature is still here and looks beautiful. The written characters are gorgeous, the language doesn't sound too bad, in every corner there is something new to learn. My friends are reliable and always willing to help, and I want to keep them forever. The concept of social peace is central to Chinese society, thus conflicts and uncomfortable situations are avoided whenever possible. I feel growing quickly as a person and culturally. Clearly the country is developing at unrecorded speed through adopting strategies which are unknown to most foreign governments.
I get desperate and think of running to the airport every time I find myself unable to send/read an email or paper, or the Skype call won't work. I bought a local LeNovo computer which turned out to be a nightmare because of language/system/connection settings which refuse to be changed plus a patchwork of hardware issues still surfacing. In the lab most of the time I feel frustrated and baseline angry because I cannot easily make myself understood in too many different areas (requests, reasoning, questions, acts, etc), resulting in my generally avoiding communication. [Trivial examples. There is no equipment maintenance, nor routine of cleaning and organisation; nobody cares. Details which are usually not important: statistics; concentrations; temperature & humidity conditions; precision; light:dark regularity; brands; purity; reproducibility; authorship criteria. Nobody is responsible nor knows about anything unless when given an order.] I have had payment conflicts from the day of my arrival, and of such complexity that would feel a monograph -- at the end I hope leaving in a civilised manner with at least 80% of the agreed salary. I am never comfortable, be at home or at work, as rooms are generally cluttered and dirty (all shared) with some degree of structural damage and pests are a constant nuisance. (Mosquitoes, cockroaches, sometimes a rat.) Authorships are locally exchanged like handshakes, and my adamant refusal to join in the club has generated tension also from day 1. I must add that advisors/supervisors see themselves as emperor thus expect being covered in flattery and papers from just sporadically sitting at their desks/thrones. The university administration has provided null help for any official procedure, including translations and health/police certifications (they didn't know what should be done or where), and they will not have me asking them questions about unstable salary pay. Finally, I mentioned my friends are gold, yet jewels are indeed rare: almost everyone approaching me is openly seeking language favor, authorships or marriage, and that might get delicate when involving some expectation of a hierarchy.
I believe some of the mentioned aspects are highly dependent on circumstances, as follows: I believe US citizens (normally given top VIP treatment in China) and Europeans would have no issues with salary pay nor quality of accommodation; Western provinces or regions near Mongolia are regarded as not so safe; faculty administration is said to be more professional in the most highly developed centres such in Beijing, Nanjing, Hangzhou; there is a strong stigma against anyone who does any drugs excepting alcohol; aggressive/impolite types may find it harder to make friends and adapt; someone willing to marry a Chinese partner will culturally and socially adapt much more smoothly.
Sorry if too long. I hope my description enables someone to decide whether China is what they are searching for. I would have greatly appreciated reading about these points before coming -- I would have not decided otherwise but would have taken many specific precautions.