The overall structure of the interview process was fairly simple in that it consisted of three phone interviews (one with an HR representative and two with different people on the team that I was applying for) and one superday (five onsite interviews, including one lunch interview).
Content-wise, the first phone call was very much focused upon culture-fit. This included basic motivations for applying for the position, my closeness with League of Legends as a long-time consumer, and how I felt I could contribute to the team in a broader sense. The interviewer was really friendly and relaxed, and I even got to chat with him about my other gaming interests such as CS:GO and Super Smash Bros.
The next two phone calls were very similar to each other in that the interviewers asked me, in addition to the previously mentioned culture-fit questions, to solve fun, League-based math problems and more difficult technical questions about their field in particular. These technical questions revolved around specific, possible improvements and feedback to the currently existing system. Basically, it seemed as though they were trying to get a feel on how I approached problems and my rationalizations behind making certain steps.
After receiving the notification that I had moved on to the onsite stage of the interview process, I immediately accepted, and Riot flew me out and put me up in a very nice hotel on their dime. Not only did I get to have an informal tour of their offices, but I also got to play in their onsite PC Bang with other Rioters. The interviews were pretty informal and relaxed, and they mostly consisted of specific questions regarding my previous experience and qualifications. While somewhat daunting at first, the interviews ended up having a lot of fun side-conversations about various interests, which calmed me as the day went on. The interviewers also took the chance to explain their own experiences at the company and what the average Rioter's day was like. Overall, it feels as though culture-fit is priority over most other things at Riot, and I tend to agree because passion is what is needed to go beyond the baseline of experience and skills.