When I came to Japan, there were quite a few options: teach with a private language school like AEON, NOVA, GEOS, or ECC, become an assistant language teacher (ALT) with the Jet Programme, or be employed directly by the school via a dispatch company...
Now NOVA is out for the count, and GEOS will be soon to follow; the language school giant recently declared bankruptcy, and many foreign instructors once again find themselves out of work. Salary payments are sketchy at best, and it's anyone's guess as to when the company will begin shutting down schools to limit expenses.
Based on the currency market, the cost of living, and the absence of a plethora of jobs, I would say it's not really a good time to teach English in Japan. Granted, there were plenty of warning signs with NOVA and GEOS, and we're not really seeing them with AEON or ECC, but when half of the big four are gone, I think it's time to consider other options. Not dispatch companies, that's for sure, but consider coming in on a tourist visa and arranging private students.
Now, if you'll excuse me, I must sleep.