Pros
If you want a comfortable life, good pay for developer standards, free food, and playing video games at work, then this is the place to be. The only string attached is that you have to follow the status quo. The status quo will not be challenged. This is the land of chill if you just do your job, which isn't a bad thing for most people. Most Rioters are cool and fun people to work and hang out with. You will not be bored. This isn't a 9-5 corporate job for sure.
Cons
Let the witch hunt begin. The single biggest issue with Riot is poor management that refuses to leave because of the lack of liquidity (and can't be fired because they are great at blowing smoke). You have people who may have been good at running a 200-person company years ago but the company has outscaled them. Running a 10x bigger company come with 10x bigger problems. There are also people who are great at surviving rather than creating value. There are people with the best of intentions but an equal if not larger amount of vested people who just want to coast until the next liquidity event. If you worked at Riot for 3-4 years, you will know what triggers to push to bog things down. Bright-eyed and bushy-tailed? Don't go. If you want to move the needle, don't go. Not now, for Riot is the graveyard of ambitions. The main consideration isn't innovation, it is protecting the core asset at all costs and milking it (League of Legends). This isn't a bad thing - just a specific business decision. Want to do big things? Go join a startup instead. Bonus tip for female candidates: ask during your interviews how many female senior leaders are in the company (zero), and then consider how far you are going to rise beyond junior/mid levels. I'll leave it at that, interview as many female Rioters as you can to get a real feel of what happens.