King of MOBAs !
While the game itself is very easy to learn, there is a lot of theorycrafting that's going on behind it. If you want to enjoy League of Legends to the max, you will probably have to watch a couple of streams/videos and read a couple of guides, or just play some games with a friend that is more experienced. If you just download the game and start by yourself, it will take you a lot of time to get accustomed to the different roles, item builds, runes and masteries and you might even feel a bit lost at some points.
The only reason I give it a 9.5 is because of the buggy game client. It's unacceptable for such a big company to be unable to fix certain bugs that exist for months.