HR and any central function like IT, Legal or Finance work in a completely different timeline than the industry, so be prepared to give more than you take or face stress, regardless of that you will have to chase continuosly to get results and colleagues will completely forget about requests made, they take no ownership of responsibility for requirements from their area that solely rely on them.
Promotions are more relationship based than about performance, so you do bump into completely unqualified managers and employees a bit more often than usual in an organisation of that size. There are of course, magnificent managers as well, but really it comes down to luck.
Pay is completely uneven as well, you're not provided with a salary range and it really feels like you're haggling in a flea market to then have to compromise on what you can survive on rather than what you deserve when compared to the market. In this they prefer to pay more for outside talent as they really bank on how good you feel on the day to day and benefits are still uneven for people that have been there for a long time, to cut down on costs if you have a chance on being promoted you're not offered a new contract, just an offer letter with new job title and wages, this way "legacy people" don't get updated benefits like health care, so you are treated like a piece of furniture.
