Find out:
1. Revenue and runway before next funding round or profitability. This trumps all in product decisions. Long runway means they can invest in new platforms and techs with bet on huge growth. Short runway means getting prestige brands into the sales pipeline to woo next investment round, and leveraging technical debt to survive. Would argue tech debt burden can be estimated as a function of remaining runway.
2. Whether board members and executives still have skin in the game and holding their stock. If board is full of early shareholders who have already been made whole, chances are you aren't their next unicorn, there is no explosive growth, and they've checked out. Expect executive level bullshit politics related to their short term compensation milestones.
3. Informal network: Who went to school with/worked with whom, and whether this role will-be / needs-to-be in that fold, or out of it. If you are not in the fold, you are a dilution target, and someones tool for meeting executive compensation milestones before changing the world. Do the work and take the money, but keep your dreams in check.
IMHO, these factors are what determine the company culture.
If the company is private, check out the other companies in the lead VCs portfolio web pages and what kinds of cultures those companies have. People move between them and you can get a better data set for glassdoor searches. If the other companies suck, this one probably will too.
What makes a company a great place to work is its real opportunity for growth because that means people are growing with it, and that brings them into work everyday. This creates a trajectory that defines its culture.
Good luck.