Pros
I was able to "lane swap" from the Research department to the Production department pretty smoothly, so there's ways to open up opportunities for yourself for growth. Riot also makes it easy to transfer between games, so if you get bored of working on one game, you can search the internal job board to find openings on other teams. Also, the pay, for a gaming company, is extremely high (no stocks though, since it's privately owned).
Kontras
Leadership is in shambles; the current CEO is a former Wall Street guy who used to be Riot's President (and CFO before that), but he didn't correct the spending of his predecessor so he's dramatically cutting costs, and content quality, now that he is CEO. Most managers here are first-time managers, so it's luck of the draw if you'll get a great manager or a poor one.