Company culture went downhill because of the buy out/IPO.
Most long-term managers forced out. Massive cronyism with new management. In the old days the company was very good about promoting from within. Not anymore. Tons of new hires at the VP+ level so them and their bros can cash out on the IPO.
Tech departments are very bureaucratic.
If you figure out a better way to do something, good for you, no one is listening.
Massive technical debt that no one upstairs cares about paying. Well, if they do care, no one will give you the resources to do anything about it.
I almost forgot. The performance review process is arbitrary and upper management manipulates it to avoid giving raises. Reviews can get downgraded if your team/department has "too many" good reviews.
Preemptive rebuttal: I know this is true about reviews, I witnessed it firsthand.