I love the battle between good and evil, and I enjoy seeing evil people brought to justice. It's different than epic fantasies where the good guy and bad guy are clearly portrayed and all we (the reader) need to do is follow the narrative through the mounting tension into the epic battle at the end of the book. For me, at least half of the fun in reading a mystery comes from trying to figure out who committed the murder.
It's not easy to fabricate one of these stories... at least not in my experience. But I really enjoy putting them together. All of the behind-the-scenes work; putting the pieces into place, building the mystery, gathering the evidence, and making sure it's hidden in a way that lets the reader see it without necessarily understanding what it means... that's a chore. But it's a fun chore.
I don't particularly enjoy making characters who murder, but in a story, there has to be a bad guy... and murder is one of the worst crimes a person can commit in this day and age.
So that's why I writing a short murder mystery. More details to come soon :D