my thoughts on magic systems are that they don't necessarily have to be complicated, but they do need to be well thought out, and the ways in which people interact with the magic are always complicated, but should still make sense.
For example, right now i am developing a story that revolves around the "magic" of a god "blessing" his people with the knowledge of how they are going to die. the concept is simple, but the ramifications are enormous and need to be thought through. it would make sense for the government to train all the people destined to die in battle for war, since that where they will be when they die, but a more clever leader might send all the people destined to die of old age to war, creating a force that could be captured at worst, but never killed. and if this is a religious gift how does it tie into religion? what would the clergy think of their Lord's gift being turned into a weapon?
also, within the society, how would this knowledge of how u r going to die affect how people interact? would a person be more likely to marry a person destined to die of the plague or someone destined to be murdered? would a person destined to die of old age have a higher or lower social status then someone else? how would a person who knows they will eventually be murdered act? How would people from other cultures view this gift if it consistently proves to be accurate?
but yeah, that's what i'm working on right now. any thoughts?