this post is dated but in case anyone searches like I just did -
I thought it was a good site but I started to wonder about its legitimacy when my children's last school strategically posted positive reviews to boost the school's rating.
I decided to check a review I posted at our previous school, from 5 years ago - it was still listed as "pending" - so it never went live to the site. It was an unfavorable review, btw.
So a few days ago I contacted greatschools.org, maybe there was some problem they weren't aware of that prevented my review from posting. Still no response...
my best recommendation - check out your school of interest on greatschools.org, though only allow it minimal influence over you; perhaps it can be a guide, or a jump-off point, for your own research.
good luck, parents!