Dota 2 completely changed my life. Its a 10 player strategy game(5 v 5) with complex mechanics which keep evolving with every update(which is like all the time).
The cool thing about this game is that you need a really coordinated team to win. One game takes around 30 to 60 minutes to finish. During this time you learn to communicate and work with people. There is no space for arguments and being selfish. Its all about the team.
I'm not much of a gamer but I love dota. :)