I found the quality of the teaching was excellent. The classes were never bigger than 4 students (though I was there over winter in the low season). I attended a standard course that was 3 x 45min classes each weekday morning. I had Magic as a teacher and her style of teaching by telling stories was really great to build vocabulary and learn grammar while also learning about Chinese history and culture.
I was at Omeida Chinese Academy for 6 months from Oct 2013 to Apr 2014. I was with my wife, we both studied Mandarin there. We had a room in the school principal's house which was okay, but could be better. When we arrived we had to ask for new pillow cases because the one's given had mould on them. We experienced more mould issues near the end of our stay when the weather started to warm up again after the cold winter. This was an issue for everyone in town it seems, as most places were not built with good insulation or ventilation. The staff at Omeida were very helpful around any issues we had and I guess the mould is not directly their fault, though I hope they put in place some measures to prevent this issue in the future.
The community around the Omeida school was great. There are many foreigners around that teach at the english school and run businesses about town. This is good and bad. Good for making lots of new friends easily, but bad because you should really be practicing your Chinese instead of speaking english.
The Chinese Academy improved a lot when they brought on board a marketing manager from NZ called Sarah and a student advisor called Wanda. Sarah and Wanda together got some of the student activities running more regularly, such as student dinners, cultural classes, weekend excursions, etc. Previously these activities existed, but were less regular and not so well advertised and organised.
In all, I highly recommend attending Omeida Chinese Academy, even if just for a short time, as the students and teachers you meet will help you with countless tips for exploring both Yangshuo and the rest of China.
Keep in mind also that you can volunteer your time with the school to get food and/or accommodation either free or at a reduced price.