Teaching English in Japan is a great way to experience Japanese culture. When you are teaching English, you get to meet a cross section of Japanese People every day from school kids to salary men to housewives and retired people.
The basic requirements for getting the working visa are that you be a native speaker of English and have a University Degree. You will need to find a school to sponsor your visa unless you can get a working holiday visa.
At one time, the pay for teaching English in Japan was considered pretty good. But there have been few increases over the years and the pay is less attractive than it once was. Some schools have found ways to cut corners such as paying teachers per lesson (instead of a salary) and not paying the teacher if the student is a no-show. There have also been numerous cases where teachers have not been paid by their schools. It is important to investigate the reputation and financial situation of a school before working there.
If you are looking at teaching English as a career choice keep your options open. Other countries such as South Korea may have better pay and working conditions.