Pros
Riot has a beautiful campus that you can practically live in and the folks that maintain and staff its various facilities are the real MVP. There are real opportunities here and certain teams/orgs are making amazing stuff. This is sadly not the norm.
Cons
Management in the creative disciplines is treated as an addon. Nearly all managers are independent contributors who are given zero tools to manage and are not evaluated on their ability to manage. The result is a competitive and cliquish culture that punishes anything different and never places accountability where it belongs. Riot doesn't know the value of a dollar. On one project we invested years of time into we never got the support we needed from other teams. Despite making it clear that the success of our project hinged on a cooperative effort from the beginning, our project was allowed to march toward death with no real indication the other teams would ever fall in line. In end, a small strike team was given a few days to deliver something to us, it did not do the trick... Why let that team languish for years, wasting tons of money and time, if there was never any intent to support it? Riot is afraid to take real chances. There have been a multitude of incredible projects designed, tinkered with, and even developed that have been iceboxed out of simple fear. With no supporting data or convincing argument everything interesting and new has had its legs taken out from under it and reduced to generic commentary, or has been outright canceled. TL:DR - When it comes to career advancement the phrase "what have you done for me lately" should have the Riot logo next to it in the Dictionary. Be prepared to kill yourself just to get noticed.
