Avantages
Look, if you are reading reviews about working at Riot Games, there are probably other companies you could work for instead. I'm not saying everyone here is passionate about gaming or Esports or Riot's IP, but most people are. It feels overall inclusive, the pay is fair, there are politics but no more than you'd expect for a company of this size. If you can get a job in your field and you like Riot, go for it.
Inconvénients
Their promotion and raise structure is very demoralising. You only get promoted if a role for that level opens up in your team, so "just doing your job well" doesn't get you neither a promotion nor a raise. If you work in EMEA, there's also the typical "global vs regional" tension, where HQ will take decisions that affect everyone without it feeling like they sufficiently look feedback.