Regardless of how you choose to measure success League of Legends is up there as one of the most successful games currently on the market. The latest stats from Riot Games show that the game is continuing to grow with a massive 32 million active monthly players currently, and a peak daily concurrent number of 3 million players. Players spend 1 billion hours a month in League of Legends - if you compare that to the entire Halo series that has amassed 2 billion player hours since its launch it puts it in some perspective.
Other interesting facts are that over 90% of players are male (there's an untapped market for you), 85% are between 16-30 years old, and 60% are either enrolled in college or have completed some level of higher education.
Anyway, have a look at the full brag graphics below: