Pros
R&D is done in a consortium with IBM and others (this is public information) so if you get to work with them you'll learn some great new technology. But there is zero internal development.
Cons
Management says they want to be the #1 foundry in the world but they spend money like they're trying to be #5. The company treats workers like disposable garbage then lies and says we're competitive. Salaries are low, bonuses are almost zero, there is no stock (unless you're an exec, then you get pre-IPO restricted units), Forced ranking means 10% of employees get thrown under the bus every year no matter how good they are. There is never enough parking and no garage so you freeze in the snow in the winter and broil in the summer walking half a mile from the outer lots. The fab itself is hotter than hell - no fab on earth runs at this temperature, but some cheap idiot decided to save money on A/C in a $6B fab. How cheap are these people? There are no paper cups for coffee or water. Visitors who don't bring their own cups can't have a drink. "Hi, welcome to GLOBALFOUNDRIES, you can't have any liquid, we can't afford it".