I worked for the companies considered "the best" in our industry with Glassdoor rating >4.5 at various stages of their lifecycle. This was happening everywhere, with singular pockets of progressive parts of company that were immune to that. At worse companies you can directly observe sexual or financial relations between managers and subordinates and resulting quick path to success as well, demoralizing the rest. Tech workers are quite often blind and don't perceive it but it's like aliasing in photographs - once you see it, it cannot be unseen.
Glassdoor is fascinating for all the wrong reasons. I've now worked in charity/community, private sector, and government, for big, small and medium.
During my last switch (from private back to government), i noticed what I'll call the "reverse glass door" effect while browsing their profiles. It was weak but it was there. That is to say, if i had to take all the employers, consultancies and corporations I've had to deal with, and rank them from places I've enjoyed myself at the most to places where I would have to genuinely ask whether there was a wage they could pay me to make me work with them again, it seemed that the workplaces I considered the worst held the highest glassdoor star ratings, and my favourites have consistently been around the middle of the pack.
As a statistician I've even considered naming and investigating this effect: explicit rating systems that end up being the inverse of what they purport to be measuring, and I've got some theories as to what could be behind it (me being abnormal, such firms having the resources/need/desire to manage their image the most, high turnover and getting new people to leave such rankings during their honeymoon period), but I've not got round to doing it with any rigor...
One of the companies my sister worked at had a full time position dedicated to countering Glassdoor reviews. For every negative review posted, this employee had to post three positive ones. Suffice it to say the company had a 4.5+ rating on Glassdoor because of this.
There could also be selection bias in who you talk to based on GlassDoor ratings: if a company has a good reputation in the industry but you just weren't feeling the connection at the interview, you might be tempted to override your feelings because "everybody else likes them, so maybe there's something wrong with me".
This is a commonly-observed effect in hiring (where oftentimes candidates who get one bad interview score or who have unconventional backgrounds do better in eventual job performance, because for them to get hired despite that obvious failing, there had to be a strong subconscious fit) and in romantic relationships (where people end up marrying people who hold commonly-desired traits - wealthy, sociable, beautiful, talented, high social status, a particular race, etc. - but then end up unfulfilled because their desire to end up with "an X partner" made them overlook people who lack that characteristic but would've been a better overall fit).
OK, ignoring signal from Glassdoor, there still might be some correlation between how well the workplace is perceived (unless is some Russian/Chinese/Indian company where everybody must love the company or else) and how much you might enjoy it. Usually bosses are the main reason people quit so there is a lot of variance between different teams.
