Anyway, if you want to join the hordes of heroes duking it out in Steam's most active game, head onto its store page and click that big ol' green button to start downloading it.
As explained on the Dota 2 blog, Valve's been improving the game's infrastructure through beta and past the official launch in July. By gradually increasing Dota 2's playerbase, Valve ensured its foundations remained up to the job. So, with server upgrades and a "huge number of enhancements" recently completed, the time came to open up the game to all.
It'll be interesting to see what that does for the game's numbers: According to Valve, Dota 2 currently boasts 6.5 million unique monthly users. For comparison, Riot Games' League of Legends had 32 million monthly players as of October 2012, hitting a staggering peak of 5 million people playing at the same time in March 2013.