Well LoL has its roots in the Warcraft 3 mod, Defense of the Ancients, or DotA as many call it. I would imagine what makes it appealing is different for different people. For me, it's because I enjoy team games much more than solo games, especially competitively and rts games like Starcraft tend to be more dominated by the 1v1 matchup where LoL and DotA are 5v5. Also I enjoy the aspect of controlling one single awesome champion. There's also the fighting game esque side of it that's about counter picks and such. It's just a fun strat game if you aren't into the more actions per minute, build order dominated side of strategy and like more action.