I've actually thought about this question a lot since you first asked it. I think this question can be split into two parts:
1. How do you rank your quality of life?
2. How much do you enjoy living in China?
I think the two are vastly different questions.
I think my quality of life in China is a 9/10. Personally, besides pollution and healthcare, and even then, healthcare you can just got to a first tier city if it's a big issue. I really don't feel China is a bad place to live, especially in second and third tier cities. They're extremely cheap to live. You don't absolutely need to learn the language to be successful (although it is remarkably helpful). So, overall, and besides pollution, I think the quality of life in China is MUCH better than anything I could have in the United States or many European Countries. Taxes are much lower. My income in China is tax exempt from the U.S. I also enjoy the lack of any kind of rule of law. Some people complain about this, but frankly, I love this. Coming from a libertarian perspective, I love the grey area that is most of China. Want to start a business? Then do it. Need a business license, well, there's a guy who'll sell you one. I love the lawlessness of China. I'll be sad when it changes.
In terms of how much do I enjoy living in China, I'd give it a 7/10. First is getting used to the cultural aspects of living in China, but there's not much I can complain about. The constant smoking never bothered me (again, coming from a libertarian leaning individual, I say 'light one up!'). Sure, it gets annoying needing a VPN to go to a lot of websites, but do I really NEED to watch that video of kittens on YouTube or check my FaceBook every ten minutes? To me, needing a VPN serves as a barrier to going on the internet, and really, most of the things I do on the internet I don't absolutely need to do. Same thing with TV. I mean, how much do I really need to watch TV? Why not do something constructive like learn a hobby or focus on work?
My biggest complain about living in China is the lack of knowledge about how things work and this is my biggest annoyance. First of all, hot water does not cure cancer and second cold weather isn't why people get sick. It's like China developed without telling the regular Chinese individual how to adapt. It's like their country just developed around them and their still stuck a hundred years in the past in terms of mentality and knowledge of how things work. I don't mean this to say that Chinese are stupid, only that things that many westerns would consider 'common sense' is lost on Chinese. I put this into the 'cultural differences' category. After all, how many Chinese think foreigners lack 'common sense'? But, this cultural difference really bugs me at times.