Glassdoor can be (and is) easily tainted by submitting fake positive reviews. They have a policy of not letting employers remove negative reviews, but that doesn't stop the company from flooding with "it's a fast-paced work environment, so some people clearly can't handle the heat in the kitchen" style "positive reviews" to reframe the legitimate negative ones.
So, it can sometimes be difficult to get a proper read on signal. However, it seems to be among the best data source out there.
You have to appropriately weight the reviews. Some types of reviews tend to be heavy on negative, some positive. Glassdoor is the type of site you have to focus more on the negative reviews than the positive.
I've seen this happen. Some of my colleagues had written bad reviews for a company I had worked at. My employer found out eventually. They ended up flooding glassdoor with fake positive reviews, down to changing tone and typing style between posts to throw people off.
I love glassdoor. Sometime you see high level management on there giving frank plus and minus assessments of the business, often critical of higher levels. It's not just disgruntled departures but often current employees.
