It's a sub-genre of RTS that takes some RPG elements and dumps 2 teams into an FPS like environment, but with mostly melee and magic instead of guns. They have to defend something similar to a flag, except instead of capturing the flag you have to destroy it.
From what I remember of LoL though, almost every game contains some kind of BS that, if it wasn't hacking, certainly felt like hacking and just wasn't fun for me. Characters that can move faster whilst doing a spin attack than my speed-based character runs normally, for instance.