American here, lived in mainland China for ~17 years. It's nice, as long as you have a good job with a company that sponsors your work visa. Starting your own company and sponsoring your own work visa is also possible but much more involved.
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Biggest problem I saw/had with living there long-term was that you won't ever have a green card/PR unless you are rich, make a really big salary, or have some special Phd/awards/patents. And once you hit retirement age, you aren't eligible for a work visa. Even marrying a local Chinese can be difficult to get your PR, depending on circumstances.
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I had heard rumors of a "retirement visa" being discussed by the govt but nothing concrete as far as I know.