If you're resume-building, it shouldn't hurt. After all, it's experience.

Not unless they interview you about your experiences and you say, "Well, most of the time I just acted like a clown-monkey; making all sorts of funny sounds and faces and flailing my arms and legs like this..."

as long as your employer doesnt know how teaching is like in china, then probably wont look too bad.

thats only if you want to teach back home. Always looks bad if you wanna do any other profession. They probably call it "party year" or something, like studying bwl

I'm pretty sure that for teachers (i.e., your career back home is teaching), it probably will look good, though how good depends. If you worked at an International high school, or one of the foreign language schools, it would be much better (I worked at a foreign language high school, where the curriculum and instruction style was very similar to an American high school). 

If you want to teach ESL back home, then it would be excellent. If you want to teach high school in your home country, and your experience was at a kindergarten, or language training center, it probably wouldn't hurt, but likely won't be as impressive as if you were working at the level you want to teach at.

Everything you do in your life has some relevance later on, whether that's to impress future employers, build character, give you life experience or put you in jail. Teaching English in China, if you have given it your best responsible shot, would look great on a resume if the prospective employer gave it the consideration it was deserved!

It looks better than unemployment. It might make your resume a tiny bit more memorable. It does demonstrate a certain degree of initiative to come here to teach. But that positive effect maxes out at 1 year. Staying here beyond that first contract can look more like settling or falling into a rut if teaching isn't what you majored in or intend to do in the future. 

Put yourself in the shoes of the gatekeeper HR rep looking through resumes. His goal is to not pass along somebody who can't do the job and waste the time of the supervisor who usually conducts the 2nd round interview and probably makes the decision. The HR guy doesn't care if you are an interesting person because they'll probably never see you again, they just don't want to get bitched at for wasting someone's time.

When you go home, unless you have the education background to become a teacher anyway...you're basically going to be applying for jobs based on your degree from whenever you got it. Or for older people, whatever your prior work experience was before you came.

Now taking the initiative to go across the world for a teaching job can be a part of a great story for a resume. But it can't be the whole story because, while interesting, it doesn't do anything to separate you from the fresh graduate who just learned the stuff. To the HR guy who doesn't care if you're an interesting person or not, it's the same as someone who worked at starbucks for 3 years. If the story is "I went to China to teach and found something in my field or started a business etc" then yes that's an awesome cover letter story.  That shows initiative plus meaningful, relevant follow-through to the HR gatekeeper you need to get past to get hired. The reality is that while it is psychologically challenging to move to China to teach...it's not really an accomplishment by itself in a practical sense because pretty much anybody CAN do it. Its less something that you were able to do and more something that you were willing to do. So it doesn't really give you as much of a leg up on the pile as you might think.

It also depends on where you are applying. If I was applying for another job in China, I would leave my semester as a teacher off completely and say I was brought here by the western firm I work for now. The Chinese generally want to see that you had the background to get a job automatically because to them that's what makes you a valuable person. (more than skills, initiative and experience) They are less impressed by someone who managed to weasel their way in the back door and there can be a bit of a 'foreign trash' stigma associated with foreign teachers. When I start applying for jobs in the US, I'll take the opposite approach. Americans love the idea of someone who got where they are through shear pluck, moxie and grit more than the idea of some connected ivy-league boy getting hired automatically.

It will look good if ,and only if, you point out the pluses. Try crowd control and leadership in a class of 80 kids for example. And doing it in an English immersion environment. Patience and adaptability in stressful situations are qualities employers like to see.The ESL job isn't the point on the resume.  What is the point is the kind of transferable skills you have acquired. If you are one of those people who has mastered Cantonese or Mandarin it will be a plus as the west is experiencing more immigration and tourism from China.