I had an overall positive experience while teaching at the American School of Brasilia. I suspect that over time things will get even better, but I can only base this review on my own personal experience.
Shortly after I arrived I heard horror stories about how the school had been run in the past. However, those stories all involved the school when it was being run by a former director who recently left. The director, Mr. Dequanne, who I worked with, seemed very dedicated to solving problems from the past. I found him to be extremely effective and while he has yet to turn it into a great school, it does seem to be one that is heading in the right direction. He came from one of the best schools in Sao Paulo and wanted to do good things at the school.
My biggest complaint about the American School of Brasilia is that it doesn't have as many resources as I would have liked. The library is very limited and the computer and science equipment is not quite up to date. That said, the technical end of things is expected to improve in the future. Building up the library is obviously going to be more of a challenge.
From simply a quality of life point of view, I was very happy. The school paid for my accommodation, which was very safe and had a doorman. My salary was also high enough to afford me a very good standard of living, even though Brasilia is one of the more expensive cities in the country. Weekends the city dies and there is very little to do. But, it does give you time to travel and see the country. The staff are very open to accepting new teachers and willing to go off on day trips and longer trips.
The student body itself is very mixed. Most of the students are children of the city's elite. This is both a good and bad thing. The ones that are motivated are very motivated. The ones who are spoiled and entitled, however, are VERY spoiled and entitled and can be a problem. I'm told that there was some grade inflation in the past for some of the more well connected students, but I did not see it while I was there.
You will end up spending more time teaching than you may be used to at other schools. They expect you to work very hard during the school day. What offsets that is that you are not required to also participate in extracurricular activities. Doing so is appreciated, of course, but you can avoid it if you want to have more free time on your hands.
I do suggest that you budget a fair amount of money for travel while you are teaching here. Brasilia is a capital city and doesn't have much in terms of interesting cultural things going on. You'll probably want to fly out to Rio or Sao Paulo on a regular basis to have fun. Flights are pretty inexpensive, so this shouldn't be too much of a hardship.
Some people have complained that they felt that the city was dangerous. For me I found it to feel safer than other South American cities I've been in. This region is always going to be somewhat dangerous to foreigners, but I didn't think the risks were that bad.
As far as the general curriculum, I was not that impressed by what they had on hand. But the director gave me a great deal of freedom to develop my own curriculum and supported my teaching methods. They do have standards in place but there is little consistency for those that decide what they want to teach.
The bottom line is that while the school has had problems in the past, it seems to be working to overcome them and I had a positive experience.