I am a recent convert to LoL. I had played DoTA occasionally when it was first released and never really got the hang of it. A friend indicated a game was available that was like DoTA with all the bad bits taken away. On trying it out I was instantly hooked. I love the team aspect and laning with a good and compatable partner is awesome fun, I am not great at the high kill rates but prefer to focus on taking the towers and advancing the game working as part of the team. I like the fact that the community is normally pretty supportive, the Newbie bashers are pretty few and far between and that encourages people to play and improve.
Favourite Champion is hard to pick, in PvP I usually play Janna for that long range support but the most fun to play has to be Amunu, once you tank him up a bit with despair and a Sunfire Cloak he just ambles around doing lots of damage and getting in the middle of things, he is so versatile, you can crank up his damage, build him as a tank or just have fun and go jungling. Great fun!