The number of concurrent users in the past month enjoyed peaks that dwarfed last year's figures on Steam, with an incredible 12.2M gamers playing at the same time at one point in December. Last year enjoyed a peak of 8.5M users.
However, while the news was good for Valve from a general standpoint, its two mainstays, Defense of the Ancients 2 (DOTA 2) and Counter-Strike: Global Offensive, actually suffered fewer concurrent users over last year, though they're still the top two games in terms of online play. Rather, more users were playing a greater variety of titles, including games like Fallout 4 and Grand Theft Auto V.
Many non-Steam games fared better, though. According to the, League of Legends alone enjoys "67 million playing every month, 27 million playing every day, and over 7.5 million playing at the same time during each day’s peak play time." 7.5M dwarfs games like DOTA 2; in fact, it's twice the number of the top 100 of Steam games.