The thing that makes Moriarty so interesting is that despite the fact that he's clearly an awful person who commits crimes left and right, he's not 100% an unlikable person. In fact, he's actually sort of charming. Moriarty is the dark side of Sherlock, representing what happens when that kind of intellect is coupled with stunted emotional development, but used for evil instead of good. His plans are intricate, and he always manages to be one step ahead of everyone else. But one of the coolest aspects of Moriarty's character is that he doesn't really seem like he's that interested in being part of the Evil League of Evil or anything like that: he's just bored and really looking for a challenge.