I've recently been addicted to this game since its the closest thing to a good rts/rpg game and further more its free.
Youtube videos and such don't really represent how fun this game can be until you actually play it.
The gameplay consists of 5v5 or 3v3 against enemy players or bots. The goal is to reach the enemy nexus after destroying their defenses to win the game. Thats a simplified way of putting it.
heres their youtube channel updated weekly:
http://www.youtube.com/user/RiotGamesIncheres their site:
http://www.leagueoflegends.com/Any of you who are not playing terraria or minecraft should try this out and play with me.
voice communication is needed however so get a mic and talk over ts3 or skype.