The Writer's Spellbook

One of the most important elements of a fantasy novel or a game world is the magic system. A logical and consistent magic system will do a lot to help improve the quality of the story. Pulling a magic item out of thin air cheats both you and the reader of the opportunity to enjoy the search for the item's component parts, the challenge of acquiring the knowledge of their use, and the suspense of wondering whether it might all go wrong with disastrous results.
A better magic system means a better story, and a better story means more readers. Strong, well thought out magic is a crucial element for fantasy games. If it's too easy, there's no satisfaction. If it's too hard, that's just frustrating. A system that makes sense and gives the player that sense of wonder will make your game very popular.