Honestly, the only place where you can currently get genuine company reviews today is Blind, if you can stomach the trolling. The so-called 'kool-aid drinkers' or 'hr puppets' are called out (often humorously) all the time.

For Glassdoor, I am not surprised, this is not news. I interviewed at an awful company once which had stellar - I mean actually straight-A's 'nothing wrong here, we're the best, if God came down from heaven and founded a company, this would be it' reviews. Found out from an ex-employee after they've been acquired by the company I worked at that they were pestered daily to write positive reviews.