Dota 2 is out of beta, and releasing on time for new players to flood the servers before the International begins next month. That said, the process to get into the game is actually more difficult than it was in beta, i.e., accept an invite from any given person on Steam whose inventory is probably crawling with the things.
Valve's multiplayer online battle arena remains free-to-play, but interested players will have to queue up via this page to get in the game. Valve will roll out access in batches starting this week as it spins up more servers around the world to accommodate the growing player base.
Don't think you can sneak in if you had a beta pass and just never redeemed it, either; if you haven't played Dota 2 before, you'll need to get in line with everybody else. The invite-circumventing Early Access pack is also no longer available.
Dota 2 may be out of beta, but Valve plans to keep working on it for a long time--much like its other free-to-play game, Team Fortress 2. Mac and Linux versions will be available soon.