Work-life balance can be tricky if you aren't already used to actively managing it. There's always something going on, and it can become very easy to put in extra hours. On top of which, you'll genuinely find yourself clicking with your teammates and wanting to avoid traffic/play games after work.
Hands-down the biggest drawback though is the contractor policy. I was a temp/contractor for nearly a year and a half before being converted over to a permanent employee, and I still see coworkers who have been around longer than I have and not made the transition. These are guys who touch every department at Riot, and lay a lot of the groundwork for everyone else to do their job, and they are just stuck. Still, Riot is a cool enough company that it's worth sticking around if you have the chance, in the hopes of becoming a Full-Time Employee.
If you do not get hired on as a Full-Time Employee, you have my prayers and condolences. Riot is taking steps to address these concerns now, but really I'll believe it when I start seeing conversions on a much wider scale.