Don't see a previous thread on this... so without further ado, I introduce you to:
If you have heard of and played DotA before, then you will know what this game is like. I personally was introduced by my fellow clanmates, and now play it more than any of them
The objective of the game is simple-destroy the enemies base. How you ask? You get to choose from many kickass champions, each with their own style of combat, and advantages/disadvantages. To make them even better, you can buy items in the game for them, outside the game you can buy runes, masteries and unlock spells to make your champion that much more deadly.
How this system works is, you are a summoner, and you are matched with people who have a similar summoner level to you. When you start a game, everyone's champion is level 1. There are three "lanes" to choose from, or two for the less played map. (Only 2 maps at the moment) You work your way along these lanes to destroy the turrets and enemy champions and eventually their base. It is much much more complicated than that. As you will find if you play.
Oh, and did I mention it's FREE?
Here is a list of people playing...